215 patients admitted with acute myocardial infarction were prospectively evaluated for prognostic factors. When lymphocyte potassium concentration increased by up to twofold of normal, a high lymphocyte magnesium concentration was associated with a good prognosis. However, when the increase in lymphocyte potassium concentration was greater than twofold, the presence of a high lymphocyte magnesium made no difference to mortality. Age, the female sex, anterior wall infarction, high serum enzymes, heart failure, diabetes mellitus in females and serious arrhythmias were all bad prognostic signs.