The socialization and micromobilization approaches to participation in social movements lead to contrasting expectations about predictors of participation. The former position leads one to expect that attitudes, community memberships, and previous community memberships will predict participation. The latter leads one to expect effects of present community memberships, but calls into question the role of values and previous community memberships. In this paper, I study physician participation in a local anti-abortion campaign to trace the bases of such activity. While present community memberships appear to play a role, premedical college community plays no role. Further, while attitude variables appear to play some role, anti-abortion participants in the survey actually reject the Right-to-Life movement leadership's position on most of a series of movement-relevant issues. I interpret this finding in terms of Noelle-Neumann's concept of “the spiral of silence,” which holds that the desire to avoid isolation leads to attitude incongruent activity, when such activity appears to have community sponsorship.