The relationship of bone mineral content and level of physical activity was investigated in 83 Caucasian females, aged 30 to 85 yr. Bone mineral content was measured by photon absorptiometry at a site one-third the distance from the distal radius to the olecranon process. Anthropometric measurements were taken and percent fat estimated. Physical activity questionnaires were independently evaluated by five physical education professionals, and subjects were assigned to low (N = 19), moderate (N = 36), or high (N = 28) activity groups. A significant difference (P less than 0.05) was seen in bone mineral content and in bone mineral content divided by bone width between the most active group of women and the two less active groups, even with age and menstrual status as co-variates. Mean values for bone mineral content divided by bone width, when adjusted for age and menstrual status, were 0.622, 0.651, and 0.679 g . cm-2 for the low, moderate, and high activity groups, respectively. No difference was found between the moderate and low activity groups. Percent fat estimates and skinfold thicknesses showed that women in the high activity category were significantly leaner (P less than 0.05), although height, weight, and skeletal widths for the groups were equivalent. The data indicate that a high level of physical activity could be a factor in reducing age-related bone loss and in preserving lean body mass in women.