Political parties are prominent in legislative politics and legislative research. Using data from the 99th Congress, this article assesses the degree to which significant party behaviour – defined and operationalized as behaviour that is independent of preferences – occurs in two key stages of legislative organization: the formation of standing committees and the appointment of conferees. Four hypotheses are developed and tested. When controlling for preferences and other hypothesized effects, positive and significant party effects are rare. A discussion addresses some criticisms of this unorthodox approach and attempts to reconcile some differences between these and previous findings.