A silent mutation in B-domain of the estrogen receptor-alpha (ER B) change codon 87 (from GCG to GCC) is clinically correlated with frequent spontaneous abortion and familial history of breast cancer among Caucasian patients. However, none of the 167 Japanese female patients and 46 Japanese female healthy volunteers showed ER B variant. Therefore, this DNA polymorphism might involve a genetic racial difference, and appears not to be correlated with frequent spontaneous abortion or familial history of breast cancer at least among Japanese women.