This study examined change that occurs in persons' beliefs when they anticipate being observed discussing an issue with an individual whose position on the issue opposes their own. Subjects expected to discuss an issue with a partner who held an opposing view and was much more, more, equally, or less expert on the issue. While expecting a discussion with the equally expert partner, subjects produced more arguments countering their partner's position and supporting their own position than did control subjects, who did not expect to discuss the issue. As a consequence of this preparation for the discussion, subjects expecting the equally expert partner adopted a more extreme position opposing the partner (belief polarization) than control subjects and maintained their changed beliefs after the anticipated discussion was canceled. Subjects expecting partners less expert, more expert, or much more expert than themselves did not change their beliefs. The findings of the study were assumed to be the outcome of a social comparison process motivated by subjects' self-presentational concerns.