The effects of political news on the mass audience are usually difficult to establish empirically. Recent models of mass communication effects have held that political knowledge is a better indicator of media reception than traditional measures of exposure. This claim is tested in two studies of attitudes toward Democratic and Republican leaders during the 1996 U.S. presidential primary campaigns. The impact of messages from three types of political talk radio (PTR) is examined: Rush Limbaugh, other conservative hosts, and liberal/moderate hosts. Political knowledge and exposure to talk radio are found to be equally good predictors of attitudes toward political leaders when studied separately. However, when tested against one another, exposure is the more effective measure. Agreement between Rush Limbaugh's messages and his audience's attitudes toward political figures is consistent and strong. Biased processing of PTR content by audience members with partisan predispositions contrary to those of the host is also examined.Keywords attitude formation, biased processing, media exposure, political knowledge, political leaders, political talk radio GangHeong Lee is an assistant professor at Taegu University, Korea. Joseph N. Cappella is a Professor at the Annenberg School for Communication, University of Pennsylvania. The data reported in this article were collected as part of the political talk radio project conducted at the Annenberg School for Communication and funded by grants to Kathleen Hall Jamieson and Joseph N. Cappella from The Ford Foundation and the Carnegie Corporation of New York. The views presented are those of the authors alone.Address correspondence to GangHeong Lee via e-mail: glee@asc.upenn.edu.This article examines the effects of political talk radio (PTR) on the formation of voters' attitudes toward political leaders. Political talk radio can be defined as "call-in shows that emphasize discussion of politicians, elections, and public policy issues" (Knight & Barker, 1996, p. 2). Political talk radio was once viewed primarily as a form of entertainment, especially for the lonely (Armstrong & Rubin, 1989;Bierig & Dimmick, 1979;Turow, 1974) and for the less affluent and educated (Crittenden, 1971;Surlin, 1986). In recent years, however, PTR has grown as a major source of political information for many of its audience members. In some circumstances, it can also be a determinant of public opinion and political behavior (Knight & Barker, 1996). Researchers have tried to determine whether media exposure or political knowledge is the better measure of reception of mass communication. Political talk radio provides a good context in which to test Zaller's (1996) claims about media effects because sound 370 GangHeong Lee and Joseph N. Cappella measures of media reception are available, and variance in the content of the messages sent by hosts about political leaders is large. Under these circumstances, Zaller predicts that the effects of messages will be large when receipt of those messages is properly m...