I had high hopes that this would be another fun, AIP drive-in movie from the '70s. Not so.
First of all, it was directed by Jerry Jameson, who later went on to direct more crappy movies including AIRPORT '77 and the infamous RAISE THE TITANIC. Need I say more? Probably not, but I will anyway.
Here's the story: A guy and his wife decide to sneak away from a tour group inside a cave so they can have sex. The wife falls down a hole and the husband, trying to rescue his wife, gets bit by a bat. He goes to the hospital and begins treatment for rabies. However, before long, he starts mutating into a man-sized bat.
Basically, this is just a werewolf movie except the guy turns into a bat instead of a wolf. The make-up effects by Stanley (Stan) Winston make the guy look like a cross between Eddie Munster and a character from PLANET OF THE APES (see photo below) . . . but you don't get to see the bat-man's face very much. They make you wait until near the end of the movie (in the tradition of all those 1950s horror and sci-fi movies where you hardly see the creature until the final reel).
If you still want to see this, it is on the Midnite Movies double feature disk with THE BEAST WITHIN.