diff --git a/runtime/src/main/java/org/capnproto/PackedOutputStream.java b/runtime/src/main/java/org/capnproto/PackedOutputStream.java
index fb7f304..4cdfd0f 100644
--- a/runtime/src/main/java/org/capnproto/PackedOutputStream.java
+++ b/runtime/src/main/java/org/capnproto/PackedOutputStream.java
@@ -11,12 +11,119 @@ public final class PackedOutputStream implements WritableByteChannel {
         this.inner = output;
     }
 
-    public int write(ByteBuffer src) throws IOException {
-        this.inner.getWriteBuffer();
+    public int write(ByteBuffer inBuf) throws IOException {
+        int length = inBuf.remaining();
+        ByteBuffer out = this.inner.getWriteBuffer();
 
-        // TODO
+        ByteBuffer slowBuffer = ByteBuffer.allocate(20);
 
-        return 0;
+        int inPtr = inBuf.position();
+        int inEnd = inPtr + length;
+        while (inPtr < inEnd) {
+
+
+            if (out.remaining() < 10) {
+                //# Oops, we're out of space. We need at least 10
+                //# bytes for the fast path, since we don't
+                //# bounds-check on every byte.
+
+                out = slowBuffer;
+                out.rewind();
+            }
+
+            int tagPos = out.position();
+            out.position(tagPos + 1);
+
+            byte curByte;
+
+            curByte = inBuf.get(inPtr);
+            byte bit0 = (curByte != 0) ? (byte)1 : (byte)0;
+            out.put(curByte);
+            out.position(out.position() - bit0);
+            inPtr += 1;
+
+            curByte = inBuf.get(inPtr);
+            byte bit1 = (curByte != 0) ? (byte)1 : (byte)0;
+            out.put(curByte);
+            out.position(out.position() - bit1);
+            inPtr += 1;
+
+            curByte = inBuf.get(inPtr);
+            byte bit2 = (curByte != 0) ? (byte)1 : (byte)0;
+            out.put(curByte);
+            out.position(out.position() - bit2);
+            inPtr += 1;
+
+            curByte = inBuf.get(inPtr);
+            byte bit3 = (curByte != 0) ? (byte)1 : (byte)0;
+            out.put(curByte);
+            out.position(out.position() - bit3);
+            inPtr += 1;
+
+            curByte = inBuf.get(inPtr);
+            byte bit4 = (curByte != 0) ? (byte)1 : (byte)0;
+            out.put(curByte);
+            out.position(out.position() - bit4);
+            inPtr += 1;
+
+            curByte = inBuf.get(inPtr);
+            byte bit5 = (curByte != 0) ? (byte)1 : (byte)0;
+            out.put(curByte);
+            out.position(out.position() - bit5);
+            inPtr += 1;
+
+            curByte = inBuf.get(inPtr);
+            byte bit6 = (curByte != 0) ? (byte)1 : (byte)0;
+            out.put(curByte);
+            out.position(out.position() - bit6);
+            inPtr += 1;
+
+            curByte = inBuf.get(inPtr);
+            byte bit7 = (curByte != 0) ? (byte)1 : (byte)0;
+            out.put(curByte);
+            out.position(out.position() - bit7);
+            inPtr += 1;
+
+            byte tag = (byte)((bit0 << 0) | (bit1 << 1) | (bit2 << 2) | (bit3 << 3) |
+                              (bit4 << 4) | (bit5 << 5) | (bit6 << 6) | (bit7 << 7));
+
+            out.put(tagPos, tag);
+
+            if (tag == 0) {
+                //# An all-zero word is followed by a count of
+                //# consecutive zero words (not including the first
+                //# one).
+
+                inBuf.position(inPtr);
+
+                long inWord = inBuf.getLong();
+                int limit = inEnd;
+                if (limit - inPtr > 255) {
+                    limit = inPtr + 255;
+                }
+                while(inBuf.position() < limit && inWord == 0) {
+                    inWord = inBuf.getLong();
+                }
+
+                out.put((byte)(inPtr - inBuf.position()));
+                inPtr = inBuf.position();
+            } else if (tag == 0xff) {
+                //# An all-nonzero word is followed by a count of
+                //# consecutive uncompressed words, followed by the
+                //# uncompressed words themselves.
+
+                //# Count the number of consecutive words in the input
+                //# which have no more than a single zero-byte. We look
+                //# for at least two zeros because that's the point
+                //# where our compression scheme becomes a net win.
+
+
+                // TODO
+            }
+
+
+        }
+        return length;
     }
 
     public void close() throws IOException {
diff --git a/runtime/src/test/scala/org/capnproto/SerializePackedTest.scala b/runtime/src/test/scala/org/capnproto/SerializePackedTest.scala
new file mode 100644
index 0000000..cbf2dee
--- /dev/null
+++ b/runtime/src/test/scala/org/capnproto/SerializePackedTest.scala
@@ -0,0 +1,26 @@
+package org.capnproto;
+
+import org.scalatest.FunSuite;
+import org.scalatest.Matchers._;
+import java.nio.ByteBuffer;
+
+class SerializePackedSuite extends FunSuite {
+
+  def expectPacksTo(unpacked : Array[Byte], packed : Array[Byte]) {
+    // ----
+    // write
+
+    val bytes = new Array[Byte](packed.length);
+    val writer = new ArrayOutputStream(ByteBuffer.wrap(bytes));
+    val packedOutputStream = new PackedOutputStream (writer);
+    packedOutputStream.write(ByteBuffer.wrap(unpacked));
+
+    (bytes) should equal (packed);
+
+  }
+
+  test("SimplePacking") {
+    expectPacksTo(Array(), Array());
+    //expectPacksTo(Array(0,0,12,0,0,34,0,0), Array(0x24,12,34));
+  }
+}