Thrombolysis and percutaneous transluminal coronary angioplasty (PTCA) are kinds of procedures that can be used to restore the blood flow of previously ischemic myocardium that can be the result of excessive production of reactive oxygen and nitrogen species, such as superoxide and hydroxyl radical, hypochlorous acid and peroxynitrite. Reaction of urate with some of these potent oxidants results in allantoin production. In this study, we measured the serum allantoin levels, an oxidation product of urate, and "in vivo" marker of free radical generation in reperfusion of ischemic myocardium. After an overnight fasting state, blood samples were collected from 35 patients with coronary occlusive diseases (7 women and 28 men) and 31 healthy subjects (8 women and 23 men). Serum allantoin and urate levels were measured by a GC-MS method. Serum allantoin levels of patients on PTCA therapy (mean+/-SD, 27.4 +/- 15.2 micromol/l) and thrombolytic therapy (24.6 +/- 8.6 micromol/l) were significantly higher than those of the patients without therapy (15.8 +/- 6.2 micromol/l, p < 0.05 with PTCA and p < 0.006 with thrombolysis) and healthy controls (12.6 +/- 6.3 micromol/l, p < 0.002 with PTCA and p < 0.0001 with thrombolysis). Although serum urate levels in PTCA (380.1 +/- 72.6 micromol/l) and thrombolysis (359.5 +/- 60.0 micromol/l) were higher than those in the non-therapy patients (336.6 +/- 53.8 micromol/l) and controls (318.3 +/- 81.0 micromol/l), there were no significant differences among groups (p > 0.05). The results of the study are consistent with others which have demonstrated, higher urate levels are associated with coronary occlusive diseases. Our data support the hypothesis that generation of ROS occurs during myocardial reperfusion. Increased allantoin levels may be used as an index of increased oxidative stress during reperfusion.