Experimental diabetes was induced in rats by i.v. administration of 65 mg/kg streptozotocin. After 12 days the rats were anesthetized with ether; the hearts were excised and perfusion washed. The atria and basilar portion of the ventricle were freeze clamped, weighed and assayed for content of norepinephrine (NE), epinephrine (E) and dopamine (DA) using high pressure liquid chromatography with electrochemical detection. The serum concentration and adrenal content of NE, E and DA were assayed. Results showed a significant increase in NE and DA in diabetic rat ventricles compared to control. The serum concentration of NE was significantly increased in diabetics, while E showed no change.