Circulating concentrations of leucocyte elastase were measured in 16 adult patients undergoing cardiopulmonary bypass (CPB) with a flat-sheet membrane oxygenator. Eight patients (Group I) received the calcium channel blocker nifedipine (9 micrograms.kg-1 x h-1) during CPB. Eight patients (Group II) did not receive any calcium channel blocker during surgery and served as the control group. Elastase concentrations were measured at 7 time points: 2 before, 2 during, and 3 after CPB. The bypass procedure was associated with elevation in elastase concentrations (P < 0.001). Comparing to baseline values elastase concentrations were significantly elevated (P < 0.05) 60 min after the start of CPB and on all measurements done after CPB. Elastase concentrations correlated with the duration of CPB (rs = 0.76, P < 0.001), and were not influenced by nifedipine infusion as revealed by comparing the two groups. This study demonstrates moderate elastase release during CPB with a flat-sheet membrane oxygenator and fails to confirm inhibition of elastase release by nifedipine infusion during CPB.