22 patients suffering from acute myocardial infarction were subjected to daily blood sampling for up to 6 days after admission to hospital. 5 patients with myocardial ischaemia and chest pain, but no evidence of infarction, were similarly investigated as controls. Daily measurements of plasma cortisol, corticosterone, cardiac enzymes and urea were performed. Plasma cortisol was elevated in all except one of the infarction cases and corticosterone was raised in 13 cases. Control patients had normal levels. Infarction patients were divided into three clinical groups: uncomplicated cases, complicated and fatalities. The latter group exhibited the highest levels of cortisol and corticosterone; no significant difference was seen between the other two groups. Uraemia tended to be associated with the complicated cases, particularly the fatalities, but not with uncomplicated cases. The three groups could be differentiated statistically on the basis of plasma urea concentration.