An advertisement for Anacin aspirin during the 1940s sitcom Mary Kay and Johnny drew far more responses than expected, providing early evidence of the show's success before formal TV ratings existed.
The first American sitcom, Mary Kay and Johnny, premiered in 1947 with no available ratings data to measure its audience. A.C. Nielsen did not begin tracking TV viewership until the 1950-51 season.
In 1948 sponsor Anacin ran an ad offering free pocket mirrors to the first 200 viewers who responded. The company anticipated up to 400 letters but received around 9,000 instead.
The series ran until 1950 and produced an estimated 300 episodes, most of which are no longer available. It incorporated the real-life pregnancy of star Mary Kay Stearns and featured the couple's newborn son Christopher as a character at 10 days old.
Co-star and writer John Stearns later recalled that the infant was "TV's youngest actor at the age of 10 days."