ABSTRACT The cerebellum of the mormyrid fish consists of three major divisions: the valvula, the central lobes and the caudal lobes. Several studies have focused on the central lobes and the valvula, but little is known about the caudal lobes. The mormyrid caudal lobe includes anterior and posterior components. The anterior caudal lobe is associated with the lateral line and eighth nerve end organs whereas the posterior caudal lobe is associated with the electrosensory system. The present study examines the physiology and pharmacology of morphologically identified Purkinje cells and efferent cells in an in vitro slice preparation of the posterior caudal lobe. We found that the Purkinje cells in the posterior caudal lobe can be classified into three subtypes based on both their morphology and on their physiological responses to intracellular current injection and to synaptic inputs from parallel fibers and climbing fibers. Similarities and differences between the physiology of the caudal lobe and that of other regions of the mormyrid cerebellum and the mammalian cerebellum are discussed.