Effects of Althesin, sodium thiamylal and diazepam on single unit activities of various dorsal horn Rexed laminae were studied with an extracellular microelectrode recording technique and using decerebrate spinal cats. Althesin 100μl/kg I. V. suppressed spontaneous single unit activities of lamina 1,4,5 and 6 by 60,48,51 and 38%, respectively at 2-3 min after injection. Sodium thiamylal 5mg/kg I. V. suppressed spontaneous single unit activities of lamina 1,4,5 and 6 by 42,49,70 and 34%, respectively. Diazepam 0.5 mg/kg suppressed spontaneous single unit activities of lamina 1,4,5 and 6 by 38,72,66 and 48%, respectively. The effects of Althesin 100μl/kg on single unit activities of dorsal horn cells are compared with those of sodium thiamylal 5mg/kg and diazepam 0.5mg/kg. These drugs suppressed the activities remarkably in all Rexed laminae at 2 to 5 min. A lamina specific suppression, such as was seen in the case of ketamine hydrochloride and morphine sulfate, was not apparent. The degree of the suppression after administration of diazepam 0.5mg/kg I. V. was the largest among these drugs and recovery from the effects required the longest time. The recovery from the effect was the most rapid in the case of Althesin. There were, however, no other significant changes among these drugs.