|Groucho Marx||Dr. Hugo Z. Hackenbush|
|Allan Jones||Gil Stewart|
|Maureen O'Sullivan||Judy Standish|
|Margaret Dumont||Emily Upjohn|
|Douglas Dumbrille||J.D. Morgan|
|Sig Ruman||Dr. Leopold X. Steinberg|
Hugo Hackenbush is a veterinarian who masquerades as a lead doctor at Standish Sanitarium to aid the wealthy patient Emily Upjohn . In order to save the financially failing sanitarium and its beautiful owner, Judy Standish, Hackenbush, employee Tony and jockey Stuffy must find ingenious ways to help Gil Stewart and his inept racehorse, Hi-Hat, win the big race.