Hanna-Barbera cartoon spanning 13 episodes between 1974 and 1975. The title character, Inch High, was able to shrink in size by drinking a special potion. He used this power to solve crimes for the Finkerton Detective Agency, with the help of his niece Lori, her boyfriend Gator, and Braveheart the dog.
The show is apparently hard to catch nowadays, though I have seen episodes this year on Cartoon Network. It's worth checking out for the characters' clothing alone; Lori's vibrant 70s fashions, Gator's brown hat / red bow-tie combination and Inch's all-green trenchcoat ensemble are all fabulous. The stories move at a fair pace and feature a number of size-related gags, often reminiscent of the giant props scenes of Bill Finger-era Batman.
See http://www.toonopedia.com/inchhigh.htm for more information.