diff --git a/README.md b/README.md
index 8dcf730..7e71744 100644
--- a/README.md
+++ b/README.md
@@ -262,6 +262,19 @@ $body->read(); // throws BadMethodCallException
 $body->getContents(); // throws BadMethodCallException
 ```
 
+Besides streaming the response body, you can also stream the request body.
+This can be useful if you want to send big POST requests (uploading files etc.)
+or process many outgoing streams at once.
+Instead of passing the body as a string, you can simply pass an instance
+implementing React's [`ReadableStreamInterface`](https://github.com/reactphp/stream#readablestreaminterface)
+to the [HTTP methods](#methods) like this:
+
+```php
+$browser->post($url, array(), $stream)->then(function (ResponseInterface $response) {
+    echo 'Successfully sent.';
+});
+```
+
 #### submit()
 
 The `submit($url, array $fields, $headers = array(), $method = 'POST')` method can be used to submit an array of field values similar to submitting a form (`application/x-www-form-urlencoded`).
diff --git a/examples/stream-stdin.php b/examples/stream-stdin.php
new file mode 100644
index 0000000..4aaaa44
--- /dev/null
+++ b/examples/stream-stdin.php
@@ -0,0 +1,24 @@
+<?php
+
+use Clue\React\Buzz\Browser;
+use React\Stream\ReadableStreamInterface;
+use Psr\Http\Message\ResponseInterface;
+use React\Stream\Stream;
+use RingCentral\Psr7;
+
+$url = isset($argv[1]) ? $argv[1] : 'https://httpbin.org/post';
+
+require __DIR__ . '/../vendor/autoload.php';
+
+$loop = React\EventLoop\Factory::create();
+$client = new Browser($loop);
+
+$in = new Stream(STDIN, $loop);
+
+echo 'Sending STDIN as POST to ' . $url . '…' . PHP_EOL;
+
+$client->post($url, array(), $in)->then(function (ResponseInterface $response) {
+    echo 'Received' . PHP_EOL . Psr7\str($response);
+}, 'printf');
+
+$loop->run();
diff --git a/src/Io/Sender.php b/src/Io/Sender.php
index 871f4a6..66ecd92 100644
--- a/src/Io/Sender.php
+++ b/src/Io/Sender.php
@@ -17,6 +17,7 @@
 use React\Dns\Resolver\Resolver;
 use React\Promise;
 use Clue\React\Buzz\Message\MessageFactory;
+use React\Stream\ReadableStreamInterface;
 
 class Sender
 {
@@ -115,11 +116,15 @@ public function send(RequestInterface $request, MessageFactory $messageFactory)
             return Promise\reject(new \InvalidArgumentException('Sending request requires absolute URI with scheme and host'));
         }
 
-        $body = (string)$request->getBody();
+        $body = $request->getBody();
 
-        // automatically assign a Content-Length header if the body is not empty
-        if ($body !== '' && $request->hasHeader('Content-Length') !== null) {
-            $request = $request->withHeader('Content-Length', strlen($body));
+        // automatically assign a Content-Length header if the body size is known
+        if ($body->getSize() !== null && $body->getSize() !== 0 && $request->hasHeader('Content-Length') !== null) {
+            $request = $request->withHeader('Content-Length', $body->getSize());
+        }
+
+        if ($body instanceof ReadableStreamInterface && $body->isReadable() && !$request->hasHeader('Content-Length')) {
+            $request = $request->withHeader('Transfer-Encoding', 'chunked');
         }
 
         $headers = array();
@@ -146,7 +151,29 @@ public function send(RequestInterface $request, MessageFactory $messageFactory)
             ));
         });
 
-        $requestStream->end($body);
+        if ($body instanceof ReadableStreamInterface) {
+            if ($body->isReadable()) {
+                if ($request->hasHeader('Content-Length')) {
+                    // length is known => just write to request
+                    $body->pipe($requestStream);
+                } else {
+                    // length unknown => apply chunked transfer-encoding
+                    // this should be moved somewhere else obviously
+                    $body->on('data', function ($data) use ($requestStream) {
+                        $requestStream->write(dechex(strlen($data)) . "\r\n" . $data . "\r\n");
+                    });
+                    $body->on('end', function() use ($requestStream) {
+                        $requestStream->end("0\r\n\r\n");
+                    });
+                }
+            } else {
+                // stream is not readable => end request without body
+                $requestStream->end();
+            }
+        } else {
+            // body is fully buffered => write as one chunk
+            $requestStream->end((string)$body);
+        }
 
         return $deferred->promise();
     }
diff --git a/src/Message/MessageFactory.php b/src/Message/MessageFactory.php
index f533a20..5e734ff 100644
--- a/src/Message/MessageFactory.php
+++ b/src/Message/MessageFactory.php
@@ -17,15 +17,15 @@ class MessageFactory
     /**
      * Creates a new instance of RequestInterface for the given request parameters
      *
-     * @param string              $method
-     * @param string|UriInterface $uri
-     * @param array               $headers
-     * @param string              $content
+     * @param string                         $method
+     * @param string|UriInterface            $uri
+     * @param array                          $headers
+     * @param string|ReadableStreamInterface $content
      * @return RequestInterface
      */
     public function request($method, $uri, $headers = array(), $content = '')
     {
-        return new Request($method, $uri, $headers, $content);
+        return new Request($method, $uri, $headers, $this->body($content));
     }
 
     /**
diff --git a/tests/FunctionalBrowserTest.php b/tests/FunctionalBrowserTest.php
index 49549ac..a0511da 100644
--- a/tests/FunctionalBrowserTest.php
+++ b/tests/FunctionalBrowserTest.php
@@ -9,6 +9,7 @@
 use React\SocketClient\DnsConnector;
 use Clue\React\Buzz\Message\ResponseException;
 use Clue\React\Block;
+use React\Stream\ReadableStream;
 
 class FunctionalBrowserTest extends TestCase
 {
@@ -130,4 +131,53 @@ public function testErrorStatusCodeRejectsWithResponseException()
             $this->assertEquals(404, $e->getResponse()->getStatusCode());
         }
     }
+
+    public function testPostString()
+    {
+        $response = Block\await($this->browser->post($this->base . 'post', array(), 'hello world'), $this->loop);
+        $data = json_decode((string)$response->getBody(), true);
+
+        $this->assertEquals('hello world', $data['data']);
+    }
+
+    public function testPostStreamChunked()
+    {
+        $stream = new ReadableStream();
+
+        $this->loop->addTimer(0.001, function () use ($stream) {
+            $stream->emit('data', array('hello world'));
+            $stream->close();
+        });
+
+        $response = Block\await($this->browser->post($this->base . 'post', array(), $stream), $this->loop);
+        $data = json_decode((string)$response->getBody(), true);
+
+        $this->assertEquals('hello world', $data['data']);
+    }
+
+    public function testPostStreamKnownLength()
+    {
+        $stream = new ReadableStream();
+
+        $this->loop->addTimer(0.001, function () use ($stream) {
+            $stream->emit('data', array('hello world'));
+            $stream->close();
+        });
+
+        $response = Block\await($this->browser->post($this->base . 'post', array('Content-Length' => 11), $stream), $this->loop);
+        $data = json_decode((string)$response->getBody(), true);
+
+        $this->assertEquals('hello world', $data['data']);
+    }
+
+    public function testPostStreamClosed()
+    {
+        $stream = new ReadableStream();
+        $stream->close();
+
+        $response = Block\await($this->browser->post($this->base . 'post', array(), $stream), $this->loop);
+        $data = json_decode((string)$response->getBody(), true);
+
+        $this->assertEquals('', $data['data']);
+    }
 }