This 1 year study examined the effect of high impact and low impact activities on bone mineral density (BMD) at the lumbar vertebrae (L2-L4) in healthy, sedentary, early postmenopausal women. Fifteen subjects whose postmenopausal status was verified by the blood levels of follicle stimulating hormone (FSH) and estradiol were chosen. These subjects were tested on the following variables: BMD via dual photon absorptiometry, heart rate response to the Balke treadmill test, percent fat via skinfolds, and a 3-d dietary analysis. Subjects were matched and then assigned randomly to one of three groups: (a) a control nonexercising group, (b) a low impact exercise group, and (c) a high impact exercise group. The control nonexercising group experienced a significant linear decrease in BMD during the study (F = 12.63, P = 0.002). Both the low and high impact exercise groups maintained BMD during the study (F = 0.04, P = 0.85; F = 1.08, P = 0.31, respectively). The difference in BMD between the low impact and the high impact exercise groups was not significant (F = 0.36, P = 0.55). In conclusion, 20 min of moderate intensity low impact or high impact exercise 3 d.wk-1 for 1 yr is effective in maintaining BMD in early postmenopausal women.