Comparison of circulating monocytes from pre- and postmenopausal females with low or high bone mineral density (BMD). Circulating monocytes are progenitors of osteoclasts, and produce factors important to bone metabolism. Results provide insight into the role of monocytes in osteoporosis. We identify osteoporosis genes by microarray analyses of monocytes in high vs. low hip BMD (bone mineral density) subjects. Microarray analyses of monocytes were performed using Affymetrix 1.0 ST arrays in 73 Caucasian females (age: 47-56) with extremely high (mean ZBMD =1.38, n=42, 16 pre- and 26 postmenopausal subjects) or low hip BMD (mean ZBMD=-1.05, n=31, 15 pre- and 16 postmenopausal subjects). Differential gene expression analysis in high vs. low BMD subjects was conducted in the total cohort as well as pre- and post-menopausal subjects.