In order to determine the risk of bacteraemia from ERCP, we cultured blood specimens from 83 patients before, during and 15 min, 1, 6, 12 and 24 hours after the examination as well as in the subsequent week whenever fever occurred. No bacteraemia was found in the 20 patients who had duodenoscopy only, i.e. in whom ERCP failed. Of the 20 patients with normal biliary and/or pancreatic ducts positive culture was obtained in one patient in whom inadvertent multiple injections of contrast material into the pancreatic duct had resulted in the occurrence of a pyelogram. Four positive cultures were found amongst the 43 patients in whom an obstructive pathology in the biliary or pancreatic system was present. These data support the need of on antibiotic prophylaxis for patients with valvular heart defects.