A controlled experiment was performed in a field situation to test the hypothesis that an individual directly insulted by a communicator attempting to persuade him will show a “boomerang effect” by increasing the extremity of his initial attitude position. The field situation consisted of a park-bench discussion of a topical social issue, arranged by a public-opinion interviewer. Prepared experimental variations were introduced by one of the discussion partners, a confederate of the interviewer. In the critical variation, the confederate insulted the subject during discussion. In other variations, he tried to persuade but did not insult, or else simply gave certain arguments without intent to persuade. Attitude-change results supported the hypothesis of negative change in the insult condition. Other experimental variations were whether the insulter stayed or left following his last argument, and whether or not a crowd hostile to the insulter was present. No significant differences in attitude change were attributable to these variations. The mechanism for the obtained “boomerang effect” remains unexplained, although a “social equity” explanation has some plausibility.