The aim of this study was to investigate effects of an organophosphate insecticide, diazinon (DI), on pancreas, and possible ameliorating role of vitamins E and C. We examined both in vivo and in vitro effects of DI on serum activities of alkaline phosphatase (ALP), gamma-glutamyltransferase (GGT), amylase, and lipase enzymes. We also evaluated possible ameliorating effects of vitamins E and C combination against DI toxicity and blood levels of thiobarbituric acid reactive substances (TBARS) only in vivo. In vivo experimental groups were: control group. DI-treated group, and DI + vitamins E plus C-treated group. In vitro study groups were: control group and DI-treated group. The biochemical analyses were determined in in vitro experiments at both hour 0 and 24 while in in vivo experiments were determined only at hour 24. Lipase activity and TBARS level were found increased by DI in in vivo experiments while lipase activity was found decreased in in vitro experiments. Amylase and ALP activities were found decreased by DI in both in vivo and in vitro experiments. Also, the combination of vitamins E and C was found to partially improve these disorders. These results suggest that DI treatment causes pancreas damage via increasing oxidative stress in rats. and a combination vitamins E and C can reduce this lipoperoxidative effect. (C) 2004 Elsevier Inc. All rights reserved.