The reported experiment tested predictions made by the elaboration likelihood model (ELM). Manipulations of message processing involvement, argument strength, and favorability of source information were used to examine predicted effects on cognitive response activity and attitude change. Major study findings reveal general support for ELM predictions concerning cognitive response activity, as well as support for central and peripheral attitude change predictions. In addition, central route attitude change was influenced by message cognitions, while peripheral route attitude change was determined by both message cognitions as well as simple perceptions of the source. A theoretical interpretation of the results and implications for advertising practice are offered.