Harvey(1972)

Overview:

Elwood P. Dowd's constant companion is Harvey, a six-foot tall invisible rabbit. To his sister, his obsession with Harvey has been a thorn in her plans to marry off her daughter. However, when she decides to put Elwood in a mental institution, a mix-up occurs, and she finds herself committed instead. It's now up to Elwood and "Harvey" to straighten out the mess.