diff --git a/PInvoke/User32/WinUser.Message.cs b/PInvoke/User32/WinUser.Message.cs
index 4de894f2..6560b54b 100644
--- a/PInvoke/User32/WinUser.Message.cs
+++ b/PInvoke/User32/WinUser.Message.cs
@@ -2065,7 +2065,7 @@ namespace Vanara.PInvoke
 		[DllImport(Lib.User32, SetLastError = false, CharSet = CharSet.Auto)]
 		[PInvokeData("Winuser.h", MSDNShortId = "ms644950")]
 		[System.Security.SecurityCritical]
-		public static extern IntPtr SendMessage(HWND hWnd, uint msg, IntPtr wParam = default, IntPtr lParam = default);
+		public static extern IntPtr SendMessage(HWND hWnd, uint msg, [In] IntPtr wParam = default, [In] IntPtr lParam = default);
 
 		/// <summary>
 		/// <para>
@@ -2099,7 +2099,7 @@ namespace Vanara.PInvoke
 		[DllImport(Lib.User32, SetLastError = false, CharSet = CharSet.Auto)]
 		[PInvokeData("Winuser.h", MSDNShortId = "ms644950")]
 		[System.Security.SecurityCritical]
-		public static extern IntPtr SendMessage(HWND hWnd, uint msg, IntPtr wParam, string lParam);
+		public static extern IntPtr SendMessage(HWND hWnd, uint msg, [In] IntPtr wParam, string lParam);
 
 		/// <summary>
 		/// <para>
@@ -2135,6 +2135,40 @@ namespace Vanara.PInvoke
 		[System.Security.SecurityCritical]
 		public static extern IntPtr SendMessage(HWND hWnd, uint msg, ref int wParam, [In, Out] StringBuilder lParam);
 
+		/// <summary>
+		/// <para>
+		/// Sends the specified message to a window or windows. The <c>SendMessage</c> function calls the window procedure for the specified
+		/// window and does not return until the window procedure has processed the message.
+		/// </para>
+		/// <para>
+		/// To send a message and return immediately, use the <c>SendMessageCallback</c> or <c>SendNotifyMessage</c> function. To post a
+		/// message to a thread's message queue and return immediately, use the <c>PostMessage</c> or <c>PostThreadMessage</c> function.
+		/// </para>
+		/// </summary>
+		/// <param name="hWnd">
+		/// <para>
+		/// A handle to the window whose window procedure will receive the message. If this parameter is <c>HWND_BROADCAST</c>
+		/// ((HWND)0xffff), the message is sent to all top-level windows in the system, including disabled or invisible unowned windows,
+		/// overlapped windows, and pop-up windows; but the message is not sent to child windows.
+		/// </para>
+		/// <para>
+		/// Message sending is subject to UIPI. The thread of a process can send messages only to message queues of threads in processes of
+		/// lesser or equal integrity level.
+		/// </para>
+		/// </param>
+		/// <param name="msg">
+		/// <para>The message to be sent.</para>
+		/// <para>For lists of the system-provided messages, see System-Defined Messages.</para>
+		/// </param>
+		/// <param name="wParam">Additional message-specific information.</param>
+		/// <param name="lParam">Additional message-specific information.</param>
+		/// <returns>The return value specifies the result of the message processing; it depends on the message sent.</returns>
+		// LRESULT WINAPI SendMessage( _In_ HWND hWnd, _In_ UINT Msg, _In_ WPARAM wParam, _In_ LPARAM lParam); https://msdn.microsoft.com/en-us/library/windows/desktop/ms644950(v=vs.85).aspx
+		[DllImport(Lib.User32, SetLastError = false, CharSet = CharSet.Auto)]
+		[PInvokeData("Winuser.h", MSDNShortId = "ms644950")]
+		[System.Security.SecurityCritical]
+		public static extern IntPtr SendMessage(HWND hWnd, uint msg, [In] IntPtr wParam, [In, Out] StringBuilder lParam);
+
 		/// <summary>
 		/// Sends the specified message to a window or windows. The SendMessage function calls the window procedure for the specified window
 		/// and does not return until the window procedure has processed the message.
diff --git a/UnitTests/PInvoke/User32/User32Tests.cs b/UnitTests/PInvoke/User32/User32Tests.cs
index 478bd40b..51fd0a2a 100644
--- a/UnitTests/PInvoke/User32/User32Tests.cs
+++ b/UnitTests/PInvoke/User32/User32Tests.cs
@@ -2,6 +2,7 @@
 using System;
 using System.Linq;
 using System.Runtime.InteropServices;
+using System.Text;
 using Vanara.InteropServices;
 using static Vanara.PInvoke.User32;
 
@@ -102,10 +103,13 @@ namespace Vanara.PInvoke.Tests
 		[Test()]
 		public void SendMessageTest1()
 		{
-			throw new NotImplementedException();
+			var length = 256;
+			var sb = new StringBuilder(length);
+			Assert.That(SendMessage(FindWindow("Progman", null), (uint)WindowMessage.WM_GETTEXT, (IntPtr)sb.Capacity, sb).ToInt32(), Is.GreaterThanOrEqualTo(1));
+			TestContext.WriteLine(sb);
 		}
 
-		[Test()]
+			[Test()]
 		public void SendMessageTest2()
 		{
 			throw new NotImplementedException();