Incredible Shrinking Man, The (1957) http://uk.imdb.com/Title?0050539
Directed by Jack Arnold.
Writing credits: Richard Matheson (also novel The Shrinking Man) & Richard Alan Simmons.
After an exposure in his boat to a strange mist, Scott Carey begins to shrink. His doctor is confounded. His cat attacks him. Then he accidently gets locked in the basement. His very life then becomes a battle for survival, with only his wits to overcome the liability of his size. Even spiders are huge deadly monsters.
I agree completely with ZachWZ and this is a URL for the new version: http://uk.imdb.com/Title?0249596