Originally, the scenes featuring the Loch Ness Monster were intended to be filmed in the actual Loch. A life-size prop was built which had several Nessie-like humps used to disguise floatation devices. The humps were removed, however, at Billy Wilder's request. Unfortunately, during a test run in Loch Ness, the Monster-prop sank and was never recovered. A second prop (just the head and neck) was built, but was only filmed inside a studio tank.
Originally Peter O'Toole was going to play Sherlock Holmes with Peter Sellers playing Dr. Watson, but Billy Wilder decided to go with lesser known stars instead.
With a 260-page script and a budget of $10 million, this was set to be a 165-minute Road Show picture with an intermission for comfort. It was to be the "Big One" for Billy Wilder. The shooting schedule ran for six months and resulted in a rough-cut that came in at three hours and 20 minutes. The film was originally structured as a series of very specifically structured linked episodes, each with a particular title and theme. The opening sequence was to feature Watson's grandson in London claiming his inherited dispatch box from Cox & Co. and there was also a flashback to Holmes' Oxford days to explain his distrust of women. All were shot, but deleted from the final print. So what happened? Well, it appears that United Artists suffered a number of major film flops in 1969 that pretty much scuppered the road show format for Wilder's massive project. Studio execs ordered the film to be cut to fill a regular theatrical running time, whittling it down to a 125-minute version. The episodic format made the pruning process relatively simple, so cut were the opening sequence, the Oxford flashback and two full episodes entitled "The Dreadful Business of the Naked Honeymooners" at 15 minutes and "The Curious Case of the Upside Down Room" at 30 minutes. We can only hope that the full footage can one day be restored, although a full print is not currently thought to exist.
According to Billy Wilder, since because of schedule conflicts he couldn't himself supervise the bowdlerization of the picture demanded by the Studios, he entrusted the task to the editor, Ernest Walter. Nevertheless, Wilder supposedly strongly disliked the cuts made by Walter, and couldn't re-edit the movie because all the deleted scenes were lost or thrown away. Some of those scenes are available today, but never with both the audio and the video intact.
At the request of director Billy Wilder, 'Miklós Rózsa (I)' adapted music from his Violin Concerto as the basis for the film score, supplementing this with further original music.