diff --git a/src/mpi-base.jl b/src/mpi-base.jl
index 81f153299..b88e7ad2f 100644
--- a/src/mpi-base.jl
+++ b/src/mpi-base.jl
@@ -584,12 +584,44 @@ function Reduce{T}(object::T, op::Op, root::Integer, comm::Comm)
     isroot ? recvbuf[1] : nothing
 end
 
-function Scatter{T}(sendbuf::MPIBuffertype{T},
-                    count::Integer, root::Integer, comm::Comm)
+function Allreduce!{T}(sendbuf::MPIBuffertype{T}, recvbuf::MPIBuffertype{T},
+                      count::Integer, op::Op, comm::Comm)
+    flag = Ref{Cint}()
+    ccall(MPI_ALLREDUCE, Void, (Ptr{T}, Ptr{T}, Ptr{Cint}, Ptr{Cint}, Ptr{Cint},
+          Ptr{Cint}, Ptr{Cint}), sendbuf, recvbuf, &count, &mpitype(T), 
+          &op.val, &comm.val, flag)
+
+    recvbuf
+end
+                  
+function Allreduce!{T}(sendbuf::MPIBuffertype{T}, recvbuf::MPIBuffertype{T},
+                      op::Op, comm::Comm)
+    Allreduce!(sendbuf, recvbuf, length(recvbuf), op, comm)
+end
+
+function Allreduce{T}(obj::T, op::Op, comm::Comm)
+    objref = Ref(obj)
+    outref = Ref{T}()
+    Allreduce!(objref, outref, 1, op, comm)
+
+    outref[]
+end
+
+# allocate receive buffer automatically
+function allreduce{T}(sendbuf::MPIBuffertype{T}, op::Op, comm::Comm)
+
+  recvbuf = similar(sendbuf)
+  Allreduce!(sendbuf, recvbuf, length(recvbuf), op, comm)
+end
+
+
+function Scatter{T}(sendbuf::MPIBuffertype{T},count::Integer, root::Integer, 
+                    comm::Comm)
     recvbuf = Array(T, count)
     ccall(MPI_SCATTER, Void,
-          (Ptr{T}, Ptr{Cint}, Ptr{Cint}, Ptr{T}, Ptr{Cint}, Ptr{Cint}, Ptr{Cint}, Ptr{Cint}, Ptr{Cint}),
-          sendbuf, &count, &mpitype(T), recvbuf, &count, &mpitype(T), &root, &comm.val, &0)
+          (Ptr{T}, Ptr{Cint}, Ptr{Cint}, Ptr{T}, Ptr{Cint}, Ptr{Cint}, 
+           Ptr{Cint}, Ptr{Cint}, Ptr{Cint}), sendbuf, &count, &mpitype(T), 
+           recvbuf, &count, &mpitype(T), &root, &comm.val, &0)
     recvbuf
 end
 
diff --git a/src/win_mpiconstants.jl b/src/win_mpiconstants.jl
index 9daecd3bd..f5023c7f3 100644
--- a/src/win_mpiconstants.jl
+++ b/src/win_mpiconstants.jl
@@ -86,5 +86,6 @@ const MPI_WAIT = (:MPI_WAIT, "msmpi.dll")
 const MPI_WAITSOME = (:MPI_WAITSOME, "msmpi.dll")
 const MPI_WAITANY = (:MPI_WAITANY, "msmpi.dll")
 const MPI_CANCEL = (:MPI_CANCEL, "msmpi.dll")
+const MPI_ALLREDUCE = (:MPI_ALLREDUCE, "msmpi.dll")
 
 bitstype 32 CComm
diff --git a/test/test_allreduce.jl b/test/test_allreduce.jl
new file mode 100644
index 000000000..442568d4f
--- /dev/null
+++ b/test/test_allreduce.jl
@@ -0,0 +1,29 @@
+using Base.Test
+using MPI
+
+MPI.Init()
+
+comm_size = MPI.Comm_size(MPI.COMM_WORLD)
+
+send_arr = Int[1, 2, 3]
+recv_arr = zeros(Int, 3)
+
+MPI.Allreduce!(send_arr, recv_arr, MPI.SUM, MPI.COMM_WORLD)
+
+for i=1:3
+  @test recv_arr[i] == comm_size*send_arr[i]
+end
+
+
+val = MPI.Allreduce(2, MPI.SUM, MPI.COMM_WORLD)
+@test val == comm_size*2
+
+vals = MPI.allreduce(send_arr, MPI.SUM, MPI.COMM_WORLD)
+for i=1:3
+  @test vals[i] == comm_size*send_arr[i]
+  @test length(vals) == 3
+  @test eltype(vals) == Int
+end
+
+MPI.Barrier( MPI.COMM_WORLD )
+MPI.Finalize()