Inserting GUID into SQL Server

I have a stored proc were I want to insert a GUID (user id) into a table in MS SQL but I keep getting an error about the hyphen '-' that is part of the guid value, here's my proc defined below;

@userID uniqueidentifier,
@bookID int,
@dateReserved datetime,
@status bit

INSERT INTO Reservation(BookId, DateReserved, [Status], UserId)
VALUES (@bookID, @dateReserved, @status, @userID)

But when I put single quotes around the value if the stored proc is executed in Management Studio, it runs fine. How can I handle the guid insertion without problems from my stored proc?

Thanks guys.

Update Here's the sql exec

DECLARE @return_value int

EXEC    @return_value = [dbo].[usp_ReserveBook]
    @userID = AE019609-99E0-4EF5-85BB-AD90DC302E70,
    @bookID = 7,
    @dateReserved = N'09/03/2009',
    @status = 1

SELECT  'Return Value' = @return_value

Here's the error message

Msg 102, Level 15, State 1, Line 5
Incorrect syntax near '-'.