This paper investigates the potential effectiveness of counter advertising in influencing the buying habits of a convinced audience. One month before the actual study, 109 subjects indicated a brand preference in a consumer questionnaire. The subjects were randomly assigned to groups that viewed one of the following: (1) a pro-Bayer aspirin commercial, (2) a counter-Bayer aspirin commercial, (3) both pro- and counter-Bayer commercials, and (4) neutral commercials. Positive and negative attitudes were assessed immediately following the commercials, and again two weeks later. The research concludes that a single advertisement does not cause notable change of attitude in subjects who initially indicated a preference for a particular brand. (MAI)