Generally, the time from the onset of acute myocardial infarction (MI) to peak serum creatine kinase (CK) activity is short in patients with acute MI after successful reperfusion. However, in some patients peak CK is observed more than 16 hours after the onset of acute MI despite successful reperfusion. To elucidate the clinical characteristics of patients with late peak CK, CK activity was examined in 55 patients (mean age: 57.5 +/- 10.2 years) with initial acute anterior MI after successful reperfusion. All patients had coronary reflow (TIMI grade 3) within 6 hours after onset of acute MI and no subsequent reocclusion for at least 14 days. The patients were classified into two groups: group E, 41 patients with peak CK observed within 16 hours of onset of acute MI (mean 8.7 hours), and group L, 14 patients with peak CK observed after more than 16 hours (mean 18.7 hours). Although there were no significant differences in the time elapsed between the two groups, the mean peak CK was significantly lower in group L than in group E (2,179 +/- 861 vs 5,379 +/- 2,569 mU/ml, p < 0.01). Well-developed collateral supplies to the infarcted area before reperfusion were observed more frequently in group L (79% vs 24%, p < 0.01). The sum of ST elevation in all leads before reperfusion was lower in group L (12 +/- 7 vs 20 +/- 12 mm, p < 0.01) and additional ST elevation during reperfusion was not observed in group L (0% vs 56%, p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)