Serum concentration of two products lipid peroxidation (LPO) of--conjugated dienes and dienketones--was assessed in 71 patients with exacerbation and remission of chronic pancreatitis, uncomplicated gallstone disease and with combinated pathology of pancreas and biliary tracts and in 100 healthy persons. During exacerbation of pathologic process in pancreas with the different ethiology of disease strong intensification of LPO occurs, but in period of remission LPO markers were found to be close to those in control. Postoperative complications and severe outcome in patients with gallstone disease are associated with a significant increase in LPO level in serum before reoperation. Routine clinical data in these patients detect no symptom of pancreas pathology. This finding evidenced that concentration of LPO products in the sera of patients with gallstone disease may be of great significance for diagnosis of associated pancreatitis and early predictor of outcome.