Plasma epinephrine (E) and norepinephrine (NE) levels during cardiopulmonary bypass (CPB) were studied in thirty-eight cardiac patients with various grades of NYHA classification. Striking increases of both E and NE levels after release of aortic cross clamp (stage 4) were noted. A thirteen fold increase in E (from 0.05 +/- 0.05 ng/ml to 0.62 +/- 0.48 ng/ml) and sixfold increase in NE (from 0.21 +/- 0.18 ng/ml to 1.26 +/- 0.78 ng/ml) occurred from prebypass (stage 1) to stage 4. The values of E and NE were peaked at stage 4 and rapidly decreased after heart beating (stage 5). At chest closure (stage 7), E returned to close to prebypass control (stage 1) value, however NE remained still in moderately high level. Patients were divided into three groups: The mild group (NYHA class I and II, fourteen patients), the ill group (NYHA class III and IV, nineteen patients) and the IABP group (IABP support since prior to CPB due to unstable angina and ventricular septal perforation, five patients). Whereas E value at either stage 4 or stage 5 in the mild group was statistically significantly higher (p less than 0.05) than each E value at corresponding stages in the ill group. NE value at each stage 3 (prior to aortic cross clamp), stage 4 or stage 5 in ill group significantly higher than each NE value at same stages in the mild group respectively. These data suggest that depletion of E and compensatory increase of NE in the ill group may be occurred during CPB.(ABSTRACT TRUNCATED AT 250 WORDS)