Organophosphate poisoning is a common cause of severe morbidity and mortality among patients admitted to emergency departments. Tissue damages as a consequence of organophosphate poisoning are frequently reported, but preventing this potentially severe complication has not been the subject of much research. We tested whether interleukin-10, a cytoprotective agent, could prevent or diminish pathological signs of tissue damages caused by organophosphate poisoning. Thirty rats were divided into three equal groups (n = 10). Group I (sham) did not receive any agent during the experiment. Group 2 (control) received 0.8 g/kg of fenthion intraperitoneally, followed by 6 ml/kg of intraperitoneal normal saline 30 min. and 3 hr later. Group 3 (treatment) received 0.8 g/kg of fenthion intraperitoneally, followed by 2 mu g/kg of interleukin- 10 intraperitoneally 30 min. and 3 hr later. All rats were killed under anaesthesia after 6 hr and tissue samples were obtained from liver, kidneys and lungs. Even organophosphate poisonings do not cause significant clinical problems; several degrees of damages could be observed in liver, kidneys and lungs. These damages could be reduced by interleukin-10 treatment.