Twenty-eight college female volunteers, 18 to 24 years of age, were studied to determine their bone mineral density and hormonal status following 10 months of supplementation with boron. Seventeen of the subjects were college athletes (A) who participated in either varsity basketball, tennis, track, triathlons, or volleyball. Eleven eumenorrheic subjects were placed in the sedentary group (S). All athletes were eumenorrheic, except for two, who were amenorrheic. The subjects were randomly assigned to either a placebo (cornstarch) or 3 mg of Tri-Boron (Twin Labs, Ronkonkoma, NY) per day. The study was single blind; the placebo and boron supplements were identical in appearance. The subjects' maximal oxygen consumption (V02max) was assessed at month 0 only, in order to compare the athletes' aerobic capacity to that of the sedentary group. Subjects were measured at time 0 and 10 months for the following: average daily food intake, bone mineral density, plasma 1,25-dihydroxyvitamin D3, and plasma alkaline phosphatase. The following parameters were determined at 0, 6, and 10 months: serum 17-Beta estradiol, progesterone, and testosterone, and percent body fat, and body weight. The athletes had a significantly greater V02max (p < 0.05) than the sedentary group. There were no differences between the A and the S groups' food intake as measured in kcals, protein, fat, carbohydrate and fiber content. Although average body weight did not differ between activity groups, the athletes had a significantly lower (p < 0.05) percent body fat than the sedentary group. The athletes showed a slight increase in bone mineral density, whereas the sedentary group showed a slight decrease. The difference between these changes was significant (p < 0.05) between the activity groups. Furthermore, the athletes showed a slight increase in plasma 1,25-dihydroxyvitamin D3, while the sedentary group showed a decrease in this measure; the difference between these changes also proved to be significant (p < 0.05) between activity groups. There were no significant differences in plasma alkaline phosphatase values. Serum 17-B estradiol and testosterone values exhibited a significant (p < 0.05) increase for all groups combined at 6 months. There were no significant changes observed in serum progesterone. Although significant changes were observed in some of the variables measured, none of the changes were a result of the boron supplementation.