AIM: To study the effects of mu and kappa opioid receptor agonists and antagonists on the isolated colon strips of rats with cathartic colon. METHODS: Cathartic colon model was established by feeding rats with contact laxatives, and effects of mu and kappa opioid receptor agonists and antagonists on electricitystimulated contraction of isolated colon strips of rats with cathartic colon were observed. RESULTS: Compared with control group, exogenous mu and kappa agonists inhibited significantly electricity-stimulated contraction of strips of cathartic colon (8.50