A substantial body of cross-sectional data and a smaller number of intervention trials generally justify optimism that regular physical activity benefits the skeleton. We conducted an 8 month controlled exercise trial in a group of healthy college women (mean age = 19.9 years) who were randomly assigned to a control group or to progressive training in jogging or weight lifting. We measured the following variables:​ bone mineral density (BMD) of the spine (L2–4) and right proximal femur using dual-energy x-ray absorptiometry, dynamic muscle strength using the 1-RM method, and endurance performance using the 1.5 mile walk/run field test. A total of 31 women completed the 8 month study. For women completing the study, compliance, defined as the percentage of workout sessions attended, was 97% for the runners (range 90–1009/0) and 92% (range 88–100%) for the weight trainers. Body weight increased by approximately 2 kg in all groups (p < 0.05). Weight training was associated with significant increases (p < 0.01) in muscle strength in all muscle groups. Improvement ranged from 10% for the deep back to 54% for the leg. No significant changes in strength scores were observed in the control or running groups. Aerobic performance improved only in the running group (16%, p < 0.01). Lumbar BMD increased (p < 0.05) in both runners (1.3 ± 1.6%) and weight trainers (1.2 ± 1.8%). These results did not differ from each other but were both significantly greater than results in control subjects, in whom bone mineral did not change. No measure of bone mineral at the proximal femur changed significantly in any group. These results demonstrate that 8 months of supervised progressive training in either running or resistance exercise modestly increases lumbar spine mineral in young women.