Sixteen adults undergoing cardiac surgery were studied with respect to postoperative levels of zinc in plasma and urinary excretion of zinc. The preoperative plasma concentrations of zinc were normal. On the first postoperative day the mean for the series had fallen from 15 to 7.2 mumol/l. A gradual rise followed, and on the fifth day all patients had plasma zinc above the lower limit of normal range. The urinary excretion of zinc was significantly increased on the first, second and fifth days after surgery. The mean total of zinc in the urine during five days was 67 mumol. The short-term fall in plasma zinc level had no discernible effect on wound healing. It was therefore apparently harmless and did not indicate a need for zinc supplementation.