Acute edematous pancreatitis was induced in conscious rats by intravenous infusion of cerulein at a supramaximal dose of 7.5 micrograms/kg/h during 6 h. The most important finding of our study was a marked decrease in the protein and non-protein content of sulfhydryl groups parallel to an evident elevation in the malondialdehyde concentration in pancreatic tissue. The presented data suggest that in cerulein-induced acute pancreatitis in rats, oxygen radicals mediate increased peroxidation reactions which are accompanied by depletion of nonenzymatic sulfhydryl-containing free radical scavengers. The above phenomenon contributes to a disturbance in thiol metabolism resulting in serious diminution of pancreatic protein sulfhydryl compounds.