The aim of this study was to evaluate the serum behavior of human pancreas-specific protein/procarboxypeptidase B (hPASP/PCPB) in the early phases of acute pancreatitis, and to calculate its sensitivity and specificity in comparison with those of serum amylase and lipase in the diagnosis of this illness. Twenty-six acute pancreatitis patients were studied; the pancreatitis was of biliary origin in 11, due to alcohol abuse in 8, and due to other causes in 7. Sixteen patients had mild pancreatitis and 10 the severe form of the disease. Thirty-one patients with nonpancreatic acute digestive diseases were also studied. Serum concentrations of hPASP/PCPB, amylase and lipase were determined in all subjects on admission to the study as well as daily for the following 5 days in acute pancreatitis patients. All patients with acute pancreatitis had abnormally high serum hPASP/PCPB, amylase and lipase concentrations on the first day of admission. On the sixth day of the disease, 76% of acute pancreatitis patients had abnormally high serum concentrations of hPASP/PCPB, whereas only 48% (p < 0.05) had elevated serum amylase and lipase. No differences in serum levels of hPASP/PCPB, amylase or lipase were found between patients with alcoholic pancreatitis and those with other etiological forms of the disease, or between those with mild and severe forms of pancreatitis. The specificity of the three serum pancreatic protein assays, calculated on the 31 patients with nonpancreatic acute digestive diseases, was 90% for both hPASP/PCPB and lipase, 75% for amylase.(ABSTRACT TRUNCATED AT 250 WORDS)