Abstract: Objective To investigate the effects of lead exposure on nitrerg ic neurons of ileum in growing rats in order to provide exper imental ev idences for revealing the poison mechanism of angina abdominalis in lead poisoning.Methods 75 male six-week old r ats were randomly divided into five groups.There were 15 rats in each group.The rats of fourexper mental groups were poisoned by intragastr ic administr at ion with 15,30,45,90 mg/kg lead acetate once a day.The control group rats were intragastricly administered with equal volume double distilled water once a day.Furthermore,rats in each group were stochastically divided into three subg roups,and the subgroups were marked with numbers in turn.On the ten th、30th、90th day o f the ex periment,lead concentration of blood was assay ed for the rats in homolgous subgr oups.The B-nicotinamide-adenine dinucleotide phosphate(B-NA DPH)histochemical method was used to study nitrergic neurons of ileum.Results With ex tension of lead exposure and the increase of lead dosage,the lead concentration in blood of growing rat increased gradually.However,the number and activity of ileum nitric oxide synthaes(NOS)positive neurons decreased gradually.There were negative correlation between blood lead concentr ation and the number of NOS positive neurons and positve correlation between blood lead concentration and the average value of gray scale of NOS positive neurons.Conclusion The activity of NOS of nitrergic neurons and the number of nitrergic neurons in ileum decrease with lead ex posure and the decrease is influenced by the dosage and time effect of lead exposure.