We report myocardial catecholamine levels in primate ventricles assayed by high-pressure liquid chromatography with electrochemical detection. The norepinephrine content of the left ventricles of 11 monkeys (four rhesus and seven cynomolgus) was 1391 +/- 362 ng/gm (+/-SD) with a definite gradient from base (highest) to apex (lowest concentration). Dopamine and epinephrine were present in much lower concentrations (51.8 +/- 24.5 ng/gm and 59.2 +/- 20.0 ng/gm, respectively), but were similarly distributed throughout the left ventricle. There was considerable variation in norepinephrine concentration between animals, but the dopamine/norepinephrine ratio was very consistent within a given animal, averaging 3.7% +/- 1.4%. These values are probably indicative of what normal concentrations of catecholamines are likely to be in humans, and provide a basis for interpretation of results obtained in disease studies.