Serum concentrations of calcium, magnesium, potassium and phosphate can be lowered experimentally by adrenaline, which also can stimulate the secretion of parathyroid hormone (PTH). In order to evaluate the possible clinical importance of these mechanisms serial blood samples were drawn during the first three hospital days in 26 patients with acute myocardial infarction (AMI), a condition known to increase plasma catecholamine levels. During the study period there were no consistent significant changes of the serum electrolytes. The serum PTH levels, however, were significantly raised in the AMI patients already on admission and did not normalize during the observation time. The PTH concentrations were unexplained by infarct size, concomitant diseases or medication. These findings suggest that PTH could be an independent risk factor for AMI.