 Principal filming began the last week of August 1942 . The entire picture was filmed on a sound stage , with no location shooting . Hepburn had already begun her extramarital affair with Spencer Tracy , and the production was notorious for the ways in which Hepburn doted on Tracy . Tracy drank heavily during the shoot , and Hepburn was his constant guardian , nurse , maid , and gofer during this time . She tried to keep him out of the bars , assisted him when he was drunk , reinforced his ego , and ran lines with him . However , Hepburn continued to be upset by the script , and dealt with this problem by isolating herself from friends and family in order to concentrate on her interpretation of the role . 
