This study aimed to investigate the protein peroxidation process in cerulein induced acute pancreatitis. Eighteen rats were divided into three equal groups: group 1 acted as control rats had intraperitoneal injection of 0.9% NaCl, in group 2 and 3 rats had injection of cerulein 40 micrograms kg-1 for 3 or 6h of induction period respectively. Protein carbonyls which reflect peroxidative damage were found to be increased after 3h up to 2.53 +/- 0.49 comparing to 1.05 +/- 0.17 in control group and returned to control level 0.95 +/- 0.04 after 6h. These data suggest that during acute pancreatitis free radicals may play an essential role in protein damage. Decrease in protein carbonyls content after 6h suggests an elevated proteolysis of oxidatively damaged proteins.