We studied the in-hospital mortality and morbidity of 745 patients who had suffered a first myocardial infarction. One hundred twenty-four patients (16.6%) had nontransmural infarction and 621 (83.4%) had transmural infarction. Both groups of patients were similar in the distribution of age, sex, and coronary risk factors. Patients with nontransmural infarction had a significantly lower mortality (3% vs 11%, p<0.01) and a lower prevalence of premature ventricular complexes (81% vs 88%, p<0.05). The patients with transmural infarction were distributed evenly among the three subgroups with peak SGOT levels less than 120 units, 120-240 units and more than 240 units (31%, 34% and 35%, respectively), while most patients with nontransmural infarction (60%) had peak SGOT levels less than 120 units (p<0.0001). When the in-hospital mortality and morbidity were compared between the parallel subgroups, the prognosis of patients with the two types of infarctions was similar. This study shows that the peak SGOT level is more important than the type of infarction in determining the acute mortality and morbidity of first myocardial infarction.