The effect of increased physical activity on bone mineral density (BMD) of the lumbar vertebrae was examined in postmenopausal osteoporotic women. Thirty-five postmenopausal women, aged 53-77 years, whose BMD in the lumbar vertebrae (L2-L4) measured by dual energy x-ray absorptiometry (Norland XR-26) was below (> 30%) the young adult mean, were divided into two groups: a control group of 20 women and an exercise group of 15 women. The physical exercise consisted of daily outdoor walking and gymnastic training performed for 12 months. During the study period, all subjects were treated with calcium lactate, 2.0 g, and 1 alpha-hydroxyvitamin D3, 1 microgram, daily. Initial L2-L4 BMD was 0.611 +/- 0.045 (mean +/- SEM) g/cm2 in the control group and 0.606 +/- 0.066 g/cm2 in the exercise group (NS). In the control group, the BMD changes were -0.54 +/- 0.58% (mean +/- SEM) at 6 months and +1.00 +/- 1.29% at 12 months, compared to the baseline (P = 0.3424, by oneway ANOVA). In the exercise group, however, the changes were +1.78 +/- 0.90% and +4.48 +/- 0.93%, respectively (P = 0.0305, by two-way ANOVA). These data suggest that increased physical activity consisting of daily outdoor walking and gymnastic training can be useful in increasing lumbar BMD in postmenopausal osteoporotic women on calcium and vitamin D3 supplementation.