alpha 2HS-glycoprotein (AHSG) is a plasma protein which becomes concentrated in the organic matrix of bone. The two most common alleles, AHSG*1 and AHSG*2, give rise to three common phenotypes. A recent report showed that a group of postmenopausal white North American women with different AHSG phenotypes differed significantly with respect to their oestrogen status. We have studied variations in bone mineral density, measured by DEXA, and levels of sex hormones and biochemical markers of bone metabolism in a group of 88 post-menopausal women unselected as to their health status. Lumbar vertebral and femoral neck bone mineral density (BMD), and the free oestradiol index were all significantly higher (P < 0.05) in women with the AHSG 2 phenotype. Values of these three parameters were lowest in the AHSG 1 phenotype and intermediate in the AHSG 2-1 phenotype. Because the differences in BMD between the AHSG 2 and 1 phenotypes represent at least a 40% difference in fracture risk, the AHSG phenotype may be of some clinical relevance as a risk factor for osteoporosis.