The use of attack messages in political campaign communication has grown in recent years. This investigation posits a strategy of resistance to the influence of attack messages. A total of 341 initial and follow-up treatment interviews and 392 control interviews were completed among potential voters in a U.S. Senate campaign during October 1986. We hypothesized that political campaign messages can be designed to inoculate supporters of candidates against subsequent attack messages of opposing candidates. This prediction was supported. In addition, the results supported the hypothesis that inoculation confers more resistance to subsequent attack messages among strong political party identifiers as opposed to weak identifiers, non-identifiers, and crossovers. The results of this investigation extend the scope of inoculation theory to new domain, and at the same time, suggest a new strategic approach for candidates in political campaigns.