Peter O'Toole was originally cast as Sherlock Holmes, and Sir Laurence Olivier was cast as Dr. Watson. The two actors had not worked well together in the past, and were unable to overcome their differences for this movie.
One of the last actors cast was James Mason. Director Bob Clark had to travel to Spain, where Mason was shooting another movie, to meet with him. Mason agreed to play Watson if he could make him a serious character, not the "silly ass" buffoon which was the rule. Mason re-wrote two scenes, including the famous "pea scene."
The 19th century dockland set took two months and 50 men to construct at Shepperton Studio's largest soundstage. The set also included a replica muddy Thames River.
The original screenplay featured the real historical names of the suspects, Sir William Gull, 1st Baronet of Brook Street, and John Netley but these were changed in the film to the character names of Sir Thomas Spivy and William Slade respectively.
Publicity for this movie stated that it was the 134th Sherlock Holmes and Dr. Watson movie. The first had been Adventures of Sherlock Holmes (1905).