To determine the possibility of myocardial protection against reperfusion injury by allopurinol, 22 aortocoronary bypass patients were studied. Eight patients received allopurinol (200 mg during induction of anesthesia and 100 mg after starting extracorporeal circulation) during surgery (group B), and 14 patients served as a control (group A). Blood samples and myocardial biopsies were taken before and 10 min after aortic cross-clamping. No statistically significant difference between the two groups was observed considering gender, age, prior myocardial infarction, left ventricular end diastolic pressure (LVEDP), and aortic cross-clamp time. Preservation of cardiac tissue was assessed by the measurement of quantitative birefringence (QBR) changes upon the addition of adenosine 5'-triphosphate (ATP) plus calcium in biopsies and the need for postoperative inotropes. The synthesis of peroxides was estimated by the measurement of leukotriene B4 and C4 (LTB4, LTC4). LTB4 was below the level of detection (< 1.5 ng/l) before and after cross-clamping in both groups, while the LTC4 level for group A increased from < 1.5 to 27 +/- 17 ng/l compared to an increase of < 1.5 to 11 +/- 8 ng/l for group B after 10 min of reperfusion (p = .036). The decrease in QBR value in group A was 1.26 +/- 0.28 and 0.35 +/- 0.23 for group B (p < .003). Postoperatively, 11 out of 14 patients in group A needed inotropic support (dopamine or dobutamine), whereas two patients out of eight did so in group B.(ABSTRACT TRUNCATED AT 250 WORDS)