Combining tow fields to make a primary key

[Jeanette]

Hello all, I have a table with two fields set as primary keys to form a unique identification. I want to use these fields as a lookup column in another table and be able to enforce referential integrity. I tried doing the lookup field using only on of the primary keys, and I cannot enforce referential integrity. Can any tell how to get referential integrity by using both of my primary keys? Thanks in advance.