The alien character played by Mandy Patinkin was originally going to be named George Jetson but Hanna-Barbera wouldn't give the rights to the name. The decision to call his character 'George' in the movie was kept as an in-joke.
Jerry Goldsmith's synthetic and score was rejected early in post production for being "too weird" and replaced with music by Curt Sobel. Jerry Goldsmith's rejected score was released in Spring 2005 as a Varese Sarabande CD Club Release limited to 3000 copies.
Prior to theatrical release, Alien Nation was heavily re-edited in post production in order to be shorter. Originally it was supposed to be released in summer but due to the drastic re-editing it was released in October. Post production re-editing is also one of the reasons why Jerry Goldsmith's original score had to be removed and replaced.
Theatrical trailer shows parts of deleted fight scene between Sykes and Kipling that happens right after Harcourt overdoses and seemingly dies. In the movie Kipling is last seen groaning and regaining consciousness before his car explodes. In deleted fight scene Kipling knocks Sykes on ground and is about to kill him when George/San Francisco shoots Kipling with Sykes's handgun and kills him.