Serum levels of parathyroid hormone (PTH), calcium and albumin were measured daily for 5 days in 41 selected patients with moderate to severe acute pancreatitis. The PTH level was measured by means of a two-site immunoradiometric assay specific for the intact polypeptide. A rise in PTH level was observed more commonly in patients with a complicated or fatal outcome than in those with an uncomplicated course (14 of 16 versus six of 25 patients, P < 0.001). Although PTH levels were variable in the presence of hypocalcaemia, raised concentrations were found more frequently in patients with complications (seven of eight versus two of seven without complications, P = 0.035). This study confirms that an appropriate rise in PTH level occurs in response to the hypocalcaemic stimulus in patients with acute pancreatitis.