In this article we examine the opinion structure of Irish Labour party members and supporters. Our purpose is to test May's law of curvilinear disparity by dividing party members into two groups as outlined by Kitschelt. By focusing on ideological differences within political parties Kitschelt identifies two types of members: ideologues and pragmatists. We use two individual-level data sets: the Labour Leadership Election Study (LLES) and the Irish National Election Study (INES), to test May's law. We find some limited support for May's law and Kitschelt's extensions to this model.