In order to clarify the physiological significance of sulfate conjugation of catecholamines and the effect of continuous dopamine infusion on the conjugate formation, we measured the plasma levels of free and sulfoconjugated catecholamines during the perioperative period of cardiac operations. The study group consisted of 12 adult patients who underwent cardiac operations. There were 13 study intervals starting from a day before each operation to 72 hours after each operation for the collection of blood specimen. The plasma levels of free and sulfoconjugated catecholamines were measured by radioenzymatic assay. The plasma levels of free dopamine did not show significant change by the induction of anesthesia, but they increased rapidly after the start of dopamine infusion to the level of 7654.9 +/- 731.7 pg/ml. Thereafter, the plasma free dopamine levels remained steady during the 24 hours after operation at 7516.7 pg/ml to 8449.2 pg/ml. On the other hand, the plasma levels of conjugated dopamine increased progressively by dopamine infusion during the 24 hours after operation. The plasma levels of free adrenaline increased significantly to the level of 1049.5 +/- 117.7 pg/ml by dopamine infusion, and lasted with plateau until the 24th hour after operation at the range of 1076.8 pg/ml to 1218.9 pg/ml. Conjugated adrenaline followed a similar pattern to that of conjugated dopamine, with a progressive increase due to the infusion of dopamine. In the case of noradrenaline, free noradrenaline started to increase at the time of cardiopulmonary bypass and showed a further increase by dopamine infusion during the first hour after operation.(ABSTRACT TRUNCATED AT 250 WORDS)