Elwood P. Dowd is an affable man who claims to have an unseen (and presumably imaginary) friend Harvey — whom Elwood describes as a six-foot, three-and-one-half-inch (192 cm) tall pooka resembling an anthropomorphic rabbit. Elwood introduces Harvey to everyone he meets. His social-climbing sister, Veta, increasingly finds his eccentric behavior embarrassing. She decides to have him committed to a sanitarium. When they arrive at the sanitarium, a comedy of errors ensues. The young Dr. Sanderson mistakenly commits Veta instead of Elwood, but when the truth comes out, the search is on for Elwood and his invisible companion. When Elwood shows up at the sanitarium looking for his lost friend Harvey, it seems that the mild-mannered Elwood's delusion has had a strange influence on the staff, including sanitarium director Dr. Chumley.