We extend Ansolabehere, Snyder, and Stewart's (2001) method of measuring party influence over roll-call voting to the comparative state legislative context. Examining 27 state lower chambers, we find that overall parties exert detectable influence on 44% of all roll calls and 69% of close votes, but that the incidence of party influence varies strongly across chambers. Taking advantage of the comparative leverage the state context brings, we find that party influence responds significantly to measures of legislative careerism and state socioeconomic diversity, with majority size playing some role. The effect of preference polarization is complicated and conditioned by challenges facing the legislature, and we find results both challenging and conditionally supporting the conditional party government account.