Abstract: Objective To determine whether there were synergic effects of increasing risk of breast cancer in Chinese women between the genetic poly mo rphisms of CYP 1A1 M spI,ERA PvuI I,XbaI and reproductive factors or not.Methods The study subjects were a subset of a population-based case-control study conducted in Shanghai between Jan 1,1999 and Apr 30,20011 PCR restrictive length fragment poly mo rphism(PCR-RFLP)method was used to examine the 3 candidate polymorphisms in DNA extracted from buccal cell in 282 breast cancer cases and 298 age frequency-matched controls.Multivariate Log istic model was used to estimate the OR and 95%CI for the group who were both with reproductive factors and with change of one of the candidate genetic polymorphisms.The synergic effects(additive model)between the reproductive factors and one of 3 candidate genetic polymorphisms were estimated by Rothman's method.Results There was a statistically significant positive additive synergic effect of increasing the breast cancerrisk(OR=5.66,95%CI:3.28-9.76,S=2.05,AP=0.42,u=1.982,P<0.05)bet ween the benign breast disease history and CYP/A/M spI polymorphism.No significant additive synergic effects were observed between the 3 candidate polymorphisms and other reproductive factors.Conclusion Probably,there were additive synergic effects of increasing breast cancer risk between the benign breast disease history and CYP1A1 M spI polymorphism.