Scholars studying the effects of political disagreement on participation have advanced competing propositions and mixed evidence to bear on whether disagreement in discussion networks either mobilizes or demobilizes voters. This article proposes that the seeming contradiction is due to different conceptual definitions of disagreement. Briefly, researchers have implicitly defined and measured disagreement in the respondents' political discussion network as either: (a) competition between points of view; or (b) opposition to a person's view. This article clarifies a distinction between two forms of disagreement, integrates past insights on its effects on turnout and tests the hypothesized effects of network composition on voting, in a nationally representative sample of US adults. Results demonstrate the differential effects of supportive, mixed and oppositional discussion networks on the likelihood of participation. Implications for future research are discussed in conclusion.