Sensory representation in the catfish cerebellum was studied with physiological stimuli, with electric shocks applied to peripheral nerves and with electric shocks to central structures of the brain. Evoked field potentials and unit responses were recorded in different places in the cerebellum. In the catfish, different sensory modalities are represented by discrete, only partly overlapping areas of the cerebellum. Most units are unimodal by present criteria; only in the valvula a fraction of the units are responsive to two or more modalities. Visual and somatosensory areas are the largest and they occupy the bulk of the corpus cerebelli and the valvula. In the corpus, most of the visual units are near the midline and in the dorsal tier while the somatosensory units are more lateral and ventral. Mechanical lateral line input is represented in the eminentia granularis and the valvula. Acoustic units are found in the valvula. Electroreceptive units are recorded from the lateral lobus caudalis, and to a lesser degree, from the eminentia granularis and valvula. Sinusoidal tilting and vibration units are in the lobus caudalis pars medialis. Receptive fields of units, regardless of modality, are generally large and diffuse. Some visual units respond best to moving objects. Topographical organization of receptive fields only exists among the somatosensory units. Besides these findings of modality segregation, the features of interest for comparative neurology are the following. Most units are identifiable as Purkinje cells with a characteristic mossy fiber-granular cell pattern, and but in contrast to most experience with mammals, in response to direct brain or nerve stimulations, the simple spikes have different dynamic responses for different modalities. Some are first excited, then inhibited, others vice versa. Some units are not responsive to any sensory input we delivered. Some units not meeting the criteria for Purkinje cells meet several criteria for eurydendroid cells; they give large spikes and are influenced by sensory stimuli after relative long latencies. Complex spikes, however, were only consistently observed in some of the visual units.