Serum myoglobin (SMb) changes following acute myocardial infarction were studied in 67 patients admitted to the coronary care unit soon after the onset of symptoms (mean delay 2.8 ± 2.2 h; CK on admission < 150 iu/l). A typical rise and fall of SMb concentrations was seen in all cases. The maximum SMb level (718 ± 301 ng/ml) was reached 7.2 ± 3.7 h after admission. Return to values lower than 80 ng/ml was observed after a mean time of 36.2 ± 20.9 h. SMb peak concentration correlated significantly with both serum enzyme peak level and cumulated CK activity (r=0.64, P < 0.0001). The myoglobin release patterns were recorded in 121 patients. The twenty-four patients whose SMb levels remained higher than 100 ng/ml 48 h following admission demonstrated a higher incidence of left ventricular failure (Killip classes III and IV) and a mortality rate of 33%. Patients who died within three months following hospitalization (n=10) showed significantly more elevated myoglobin concentrations throughout the investigation period as compared to survivors (n=111). Myoglobin determined 4 h following admission correlated with serum lactate dehydrogenase activity, and high SMb levels were associated with an increased mortality rate. Our results suggest that SMb measurements might allow a stratification of patient risk as early as 9 to 12 h following the onset of myocardial infarction.