In the first season, there was one opening credit sequence made up entirely of location footage shot on tape in Chicago and a slightly different recording of the theme song. This was used for three weeks, then replaced with another opening sequence mixing live-action footage and an animated sequence. This lasted a few weeks and was replaced by yet another sequence mixing the location footage shot in Chicago and clips from episodes, ending with the tail end of the animated sequence being watched by the lead characters on TV. This third opening sequence is on all first season episodes in syndication in the United States, but the DVD versions have the appropriate sequences reinstated depending on the episode.
The NBC episodes were chopped from 24 minutes to 22 minutes when the show entered syndication. The DVD releases are the complete 24 minute lengths.