Innerspace 2?
If ever there was a movie written with an ending that screamed sequel it was this one. So why didn't it ever happend? The only reason I can think of is that ALL the main actors became too big. Dennis Quaid did the Big Easy the same year as Innerspace and followed that up with movies like DOA and Suspect. Meg Ryan blew up a couple of years later with When Harry Met Sally. Martin Short probably would've done it anyway cause his career wasn't going the way of a serious actor.
It's a shame too cause these actors seem to work well together.
BTW: I'm not one for remakes, but if they were to remake it today, it would look so much better with todays technology. Of course, the acting would probably suck. They'd probably get someone like Ashton Kutcher or Johnny Knoxville to play Jack Putter.