Abstract: Objective To study the interactive effect of serum organo chlorinere sidues and glutathione S-transferase M1(GSTM 1)on the risk of breast cancer in women.Methods Seventy newly diagnosed female breast cancer patients and 70 controls were investigated with face-to-face interview.The organochlorine residue level in serum were measured with gas chromatography(GC).Genotypes of GSTM 1 polym orphism were analyzed with multiplex allele-specific polymerase chain reaction(PCR).Results Odds ratio(OR)of breast cancer for women with high DD Tresidue level was 3 859 (95% confidence intervalCI=1.195-12.466),and the OR of GSTM 1 genetype polym orphism was 1.343(95%CI=0.3553-5.075).The OR of breast cancer for women with the two factors was 5.557(95%CI=1.633-18.903)with an interaction index(r)value of 1.237.The results showed that gene deletion type of GSTM 1 enhanced the effect of DDT residue in serum.The OR of breast cancer for women with high hexachlo rohexane(HCH)residue level was 2 7.31(95%CI=0.841-8.869),and the OR of with GSTM 1 genetype polym orphism was 1.483(95%CI=0.478-4.603).The OR of the two factors was 3.866(95%CI=1.178-12.682)with an interaction index(r)value of 1.379.There sults showed that gene deletion type of GSTM 1 enhanced the effect of HCH residues in serum.Conclusion Genetic polym orphisms of GSTM 1 and environmental DDT/HCH exposure have an interaction in the development of breast cancer.