This study investigates a particular way in which contextual priming influences advertising effects. It is proposed that prior exposure to contextual factors can prime or activate certain product attributes in consumers' knowledge structure and subsequently increase the likelihood that they interpret ambiguous product information in terms of these activated attributes, thereby affecting the overall impact of the ad. Two experiments are conducted to test the main hypothesis and eliminate potentially confounding effects of experimental tasks. The results demonstrate that the specific attributes relevant to evaluating the advertised brand vary in their accessibility as a function of the ad context, and that these variations influence brand attitudes and purchase intentions. Step-down analyses show further that the effects of priming product attributes operate mainly through brand attitudes. Theoretical and practical implications of these findings are also discussed.