Acute phase response after endoscopic retrogradic cholangiopancreaticography (ERCP) was studied in 42 patients with suspected pancreatic or biliary diseases. In uncomplicated cases acute phase response determined by serum C-reactive protein levels was rare and did not parallel the serum amylase or lipase levels. In three of the these 42 patients, post-ERCP pancreatitis developed and CRP levels elevated sharply and paralleled the degree of pancreatitis. Six additional patients outside of this prospective study with post-ERCP-pancreatitis and daily CRP determinations were used to determine the CRP-response curve in post-ERCP pancreatitis.