The first show ever to feature Rocky and Bullwinkle was Jay Ward Productions' Rocky and His Friends. It ran from September 29, 1959 to September 3, 1961 on ABC on Saturday evenings from 6:30 to 7:00. The main plot line featured Rocky, the flying squirrel, Bullwinkle, his devoted and dimwitted moose companion, and the Pottsylvanian Cold War era spies, Boris Badenov and Natasha Fatale.
When the show changed to NBC in 1961, the bigwigs insisted that it be retitled. In spite of the different title, The Bullwinkle Show simply continued the adventures of Rocky and His Friends. The syndicated shows on the air and for sale contain cartoons from both original network series.
There were 326 episodes total. Episodes 1-156 were first aired on Rocky and His Friends (ABC, 1959-1961). Episodes 157-260 and 301-366 were first aired on The Bullwinkle Show (NBC, 1961-1964).
From: Frostbite Falls: http://www.members.home.net/jw-ffp/