I am sorry, I have been leading you down the wrong path. You cannot import a dll in the IDL file, you can only import IDL, ODL and header files. So that will be your best bet. You can use the importlib() directive inside of your new type library, but the MSDN documentation recommends that you use the IDL file so that all of the items from the original file will be available to your app. If you rely on the data in teh DLL, you will only get what is in the type library (which this may also include all of the items in teh dll so it wouldn't matter). Either way I think that using the IDL file from your base project is prefectly acceptable. Build a man a fire, and he will be warm for a day Light a man on fire, and he will be warm for the rest of his life!