Under anesthesia with N2O (70%) and halothane (2-4%), complex spikes of Purkinje cells were extracellularly recorded in the nodulus and flocculus of immobilized pigmented rabbits. Optokinetic stimulation (OKS) was delivered to each eye as repetitive movements of a random dot pattern. The visual field of each eye was divided into anterior, central and posterior fields at axes 45 degrees and 135 degrees along the horizon. With OKS of the ipsilateral eye, the preferred direction of complex spike responses was: (1) forward (F) in all visual fields (F response), (2) upward (U) in both the anterior and central visual fields but downward (D) in the posterior visual field (U response), or (3) no response (N) in any of the visual fields (N response). With OKS of the contralateral eye, the preferred direction was: (1) backward (B) in both the anterior and central visual fields but N in the posterior visual field (B response), (2) U in the anterior but D in both the central and posterior visual fields (D response), or (3) N in all visual fields. Purkinje cells were classified into five categories in terms of the complex spike responses to OKS to the central visual fields of the ipsi-/contralateral eyes: F/B, F/N, U/D, U/N and N/D types. In cells with ipsi-F and/or contra-B responses, OKS delivered above the horizon induced F and/or B responses, but OKS below the horizon induced no response. In cells with contra-D response, OKS both above and below the horizon induced D responses. Cells with ipsi-U responses showed unusually complex direction selectivity: in the anterior, central and posterior fields, the preferred direction was U, U and D, respectively, above the horizon, as opposed to N, D and D below the horizon. In the nodulus, F/B and F/N type cells were localized in the ventral lamella within two distinct longitudinal zones about 0.5-1.5 and 2.5-3.5 mm from the midline, while U/D, U/N and N/D type cells were found in both the ventral and dorsal lamellae within a longitudinal zone about 1.5-2.5 mm from the midline. In the flocculus, the locations of F/N (or F/B), U/N and N/D type cells roughly corresponded to H, anterior V and R zones, respectively, as previously reported on the basis of the direction of eye movements induced by microstimulation.(ABSTRACT TRUNCATED AT 400 WORDS)