After ultrasonic treatment of rat liver mitochondria and the following sedimentation of the submitochondrial particles all the NAD-isocitrate dehydrogenase (NAD-ICDH) activity detected occurred in the supernatant fraction. The structures of internal side of the inner mitochondrial membrane proved to regulate the NAD-ICDH activity. Administration of adrenaline into rats stimulated the NAD-ICDH activity by 20-40% in mitochondria and mitoplasts measured after ultrasonic treatment. Activation of the enzyme was not observed in the supernatant fraction after sedimentation of submitochondrial particles. The data obtained suggest that inner mitochondrial membrane is a factors responsible for regulation of NAD-ICDH activity during cAMP-dependent stimulation of mitochondria by catecholamines.