Through the 1980s, political science research produced a more dynamic view of how bureaucracies respond to changing political conditions. However, much of this research ignored the complex stimulus environment within which bureaucracies operate, as well as the potentially rich bureaucratic response dynamic that can exist. We extend our previous work on the dynamics of political control of the bureaucracy by developing a model of political-bureaucratic adaptation. The model is tested with output data from four Environmental Protection Agency programs between 1979 and 1988. The results show that political-bureaucratic adaptation is indeed a more complex phenomenon than suggested by earlier research. Stimuli to bureaucratic behavior include discrete events, event progressions, and "tonal" shifts in the policy environment; bureaucratic responses can be immediate, delayed, or distributed through time in probabilistic fashion. Substantively, the results offer new insights on how political institutions affect bureaucratic behavior. They also suggest how, why, and to what bureaucracy responds.