Source and message content credibility, two characteristics of effective communications, were examined in the advertising content. A quasi-experimental design using actual retail comparative price advertisements was used to test the effects of retailers (sources) and meassages (discount levels) on the acceptance of the message. The findings support the conclusion that source and message credibility exists in retail advertising but with a major modification. Credibility is composed of two components, trustworthiness and price competitiveness. It appears that the relevant credibility components for the audience will depend on the source, the situation, and the objectives of the audience.