John Belushi was offered a role in this film numerous times but he originally turned it down. He eventually accepted the role but died shortly after. The producers were exited of having him on the poster wearing a diaper, even though no such scene appeared in the script. This was in the period Penny Marshall was supposed to direct based on a screenplay by John Hughes.
When getting a room to meet Inga, Alan is told to go to room 319 - the number on the door is shown clearly as Renato enters. When Carpenter later breaks down the door, it clearly says 302.