Acute experiments on cats showed that mild shifts in osmotic homeostasis (within physiological limits) result in modifications of the spike activity in a significant share of thermosensitive neurons of the Preoptic region (RPO); in particular, rhythmic aftereffects (RAE) are induced in these units. The neurons were identified as thermosensitive cells according to their responses to local heating/cooling (±7°C) of the pad surface of the contralateral forelimb. Osmotic stimulation was performed by infusions of 0.1–0.3 ml of 3.0 or 0.2% NaCl solutions in the a. carotis communis dextra. The RAE phenomenon more frequently developed in thermosensitive neurons after infusions of the hyportonic solution (13/34) than after hypotonic infusions (6/34), while in non-thermosensitive neurons the situation was reverse: hypotonic infusions induced RAE more frequently. Certain specificities were also observed in localization of the thermosensitive RPO neurons, in which osmotic stimulation-induced RAE was observed. The mechanisms of such induction and possible functional role of spike grouping in the activity of thermosensitive neurons are discussed.