In some situations the postmortem diagnosis of myocardial infarction is made difficult by the brief course of the fatal episode or by interferences caused by autolysis. In such cases, biochemical indices may provide a useful adjunct to morphological studies. Myosin is the main component of the contractile apparatus of muscle cells, so its determination may well be useful to evaluate myocardial injury. The purpose of the present study was to establish the diagnostic efficacy of postmortem myosin heavy chain determinations using monoclonal antibodies and to compare this data with structural findings used to diagnose acute myocardial ischaemia. We studied 105 cadavers with a mean age of 61.63 +/- 2.21 years. Cases were allocated to 1 of 7 diagnostic groups depending on the probable intensity of myocardial damage and cause of death. The highest serum and pericardial fluid values of myosin heavy chains were seen in subjects who showed morphological evidence of myocardial ischaemia. Mean pericardial fluid/serum ratios differed significantly between subjects with and without observable signs of heart damage.