The activity of deep cerebellar nuclei neurons was recorded in the alert cat and related to the respiratory cycle. Respiration-related neurons (RRNs, n = 29), located in the rostral fastigial and interpositus nuclei, were classified as inspiratory (24%) or expiratory (76%). Nine RRNs were antidromically activated from the red nucleus, but none from the inferior olive. Half of the RRNs showed well defined proprioceptive inputs of a rather broad origin. Other RRNs (27%) showed a respiration-related pattern independent of respiratory movement performance. Repeated electrical stimulation of the inferior olive exerted a synchronizing effect on the firing rate of 24% of the RRNs. It is proposed that cerebellar nuclear RRNs are involved in locomotor re-adjustments of the respiratory musculature.