Two experiments were conducted to advance our understanding of the effects of forewarning on persuasion. In Experiment 1, personal involvement, warning of message content, and distraction during the forewarning-message interval were manipulated. The results indicated that if warned subjects were personally involved with the attitude issue, they became resistant to the persuasive appeal when they were not cognitively distracted after warning. In contrast, when subjects were not personally involved, they were susceptible to the appeal regardless of levels of warning and distraction. In Experiment 2 manipulation of message strength was added to the three factors of Experiment 1. The results revealed that subjects in high involvement conditions were better able to differentiate the strength of the message (i.e., rate the strong message to be more persuasive than the weak one) than those in low involvement conditions; however, this was true only when the subjects were unwarned, or were warned but distracted. When warning was not followed by distraction, the subjects in high involvement conditions showed resistance to the strong message as well as the weak one. In low involvement conditions subjects were more persuaded in general, but when the warned were not distracted, they seemed to agree more with the strong message than with the weak one. Measurements of postmessage thoughts in both experiments indicated that subjects who showed resistance to the persuasive appeal generated more negative thoughts and fewer positive thoughts, compared with persuaded subjects. The results of the two experiments suggested that personal involvement mediates warned subjects' cognitive responding, and when message recipients are highly involved in a counter-attitudinal communication, warning of message content may trigger cognitive defending, which directs them to process the subsequent message in a relatively biased way, thus increasing resistance to persuasion. Results were discussed in the light of cognitive response approaches to persuasion (e.g., Chaiken, Liberman, & Eagly, 1989; Petty & Cacioppo, 1986). © 1992.