The aim of this study was to search for a possible association of low bone mineral density (bMD) with the PvuII and XbaI polymorphisms of the estrogen receptor (Er) gene in bulgarian women.400 bulgarian women participated in this study. bMD was measured at the lumbar spine, femoral neck and at the distal forearm. two groups were identified: women with normal bMD at both central sites (n=180) and women with low bMD at either site (n=220), designated as normal (NbMD) and low bMD (LbMD) groups, respectively. the genotype frequencies of PP, Pp, pp and XX, Xx, xx were investigated by Pcr and enzymatic digestion of the products by PvuII and XbaI.The genotype frequencies were 12% for the PP, 59% for the Pp and 29% for the pp genotypes in the NbMD, and 26%, 50% and 24% in the LbMD groups, respectively. the XX, Xx, xx genotype frequencies were 14%, 63% and 23% in the NbMD, and 33%, 50% and 17% in the LbMD groups, respectively. the various genotypes were significantly associated with bMD. the relative risk for low bMD was higher for the XbaI marker (rr=1.51) than for the PvuII marker (rr=1.35). the association between low bMD and the polymorphisms under study was described by an etiological factor of 0.28 for the XbaI marker and 0.20 for the PvuII marker.The specific XbaI and PvuII polymorphisms of the Er gene are associated with low bMD at all bMD measurement sites in the bulgarian female population. they might therefore become useful genetic markers in osteoporosis risk assessment in this specific population.