Fifty six patients admitted consecutively to the coronary care unit with ischemic chest pain participated in a controlled prospective study of acute changes in iron metabolism. Following myocardial infarction there were significant reductions of plasma iron by 8.1 mumol/L (P = 0.002), total iron binding capacity by 12.9 mumol/L (P = 0.003), and plasma transferrin by 0.70 g/L (P = 0.007). In contrast, there was a significant elevation of serum ferritin by 218 micrograms/L (P = 0.0005). The magnitude and duration of these acute changes in iron metabolism was greater in patients with higher peak serum creating kinase levels, suggesting that these changes are influenced by the extent of tissue necrosis. Comparison with the control group showed that alteration in dietary iron intake was not a significant factor. The possible mechanisms of these acute changes and their similarity to those observed in the anemia of chronic disease are discussed.