To observe the changes of mu and kappa opioid receptors in the cathartic colon of rat，and to clarify that whether opioid receptors accounts for the occurrence of slow transit constipation(STC)．Methods：The cathartic colon model of rat was made by feeding with laxatives．The activity of mu and kappa opioid receptors in the cathartic colon of rat was measured by radio-ligand binding assay，Results：Compared with the control group，the maximal binding capacity(Bmax)and affinity(Kd)of mu opioid receptor in cathartic colon group were significantly increased(207.00±22.90 fmoL/mg·p vs 82.00±14.23 fmol／mg·p．P<0.01；3.30±0.45 mmol／L vs 2.40±0.57 mmol／L，P<0.05)．The maxi-mal binding capacity ofkappa opioid receptor also showed a great increase(957.00±102.41 fmol／mg·p vs 459.00±52.41 fmol／mg·p，P<0.01)，but 13o significant diference of afinity was found between the two groups Conclusion：The mu and kappa opioid receptors may be involved in the functional disorders of cathartic colon，