Online surveys were conducted to determine the impact of endorser credibility, endorser effectiveness, and consumers' involvement in direct-to-consumer advertising. In a randomized posttest only study, using the elaboration likelihood model, survey participants (U.S. adults) were either exposed to a fictitious prescription drug ad with a celebrity or a noncelebrity endorser. There was no significant difference in credibility and effectiveness between the celebrity and the noncelebrity endorser. High involvement consumers viewed the ad more favorably and exhibited significantly stronger drug inquiry intentions during their next doctor visit. Further, consumers' involvement did not moderate the effect of celebrity endorser.