I have imported an AIFF file into a track in Garageband. Then I used some plug ins to get the sound I wanted. This went ok. But when I export the song to disk (mp3), none of the changes I made in Garageband go with it. It sounds exactly the same as when I imported it. Am I missing something?

If you can hear the added plug-in effects when you play the song in GB then they should be in the exported file as well. Maybe a more detailed description of what you did will point up a missed step, though off the top of my head I can't imagine what that would be (Maybe forgetting to save the changes, then re-opening the file and exporting? Or maybe you've grabbed the wrong file -- the original instead of the exported version?).. Sorry if that's too simplistic -- I don't know how well-versed you are in GarageBand, so I've attached a link to a GB course up top, just in case that might be of any help..

Yes I can hear the added effects when I play the song in Garageband. I exported to a file on the desktop (the only file there so I know I didn't grab the wrong file. I simply drag and dropped the file into a track in GB then applied the effects then exported. I'll try closing the file and saving the changes and reopen and export again to see if that works. Thanks for the reply!