The effects of boron supplementation on blood and urinary minerals were studied in 17 female college athletes and 11 sedentary college control subjects. The subjects were similar in age (19.8 ± 1.4 and 20.3 ± 1.1 years for athletes and sedentary groups, respectively) and weight (61.8 ± 9.1 and 59.6 ± 10.5 kgs for athletes and sedentary groups, respectively). The athletic subjects had lower percent body fat averages (20.6 ± 5.6 and 25.8 ± 6.5 %, respectively, (p < 0.05)) and higher aerobic capacities (2.9 ± 0.5 and 2.1 ± 0.4 L O₂*min₋₁, respectively, (p < 0.05) than sedentary controls. No differences in dietary intake were observed. Serum phosphorus levels were lower in boron supplemented subjects than in subjects receiving placebos (p < 0.05) and were lower during final analysis than during baseline analysis. A group-supplement interaction was noted with serum phosphorus also (p < 0.05). In the sedentary group, boron supplementation lowered serum phosphorus and placebo supplementation elevated serum phosphorus. In the athletic group, no changes in serum phosphorus were observed due to supplementation. Serum magnesium was greatest in the sedentary controls supplemented with boron and increased with time in all subjects (p < 0.05). Again, a group-supplement interaction was observed with serum magnesium; exercise in boron supplemented subjects lowered serum magnesium (p < 0.05). In all subjects, calcium excretion increased over time (p < 0.05) and in boron supplemented subjects boron excretion increased over time (p < 0.05). In conclusion, boron supplementation affected serum phosphorus and magnesium and the excretion of boron in the urine. The significance of these findings in relation to overall mineral status, bone mineral density, and exercise in college female athletes needs further investigation. It is possible that increasing the intake of foods high in boron may be found to be beneficial in the treatment and/or prevention of metabolic bone disorders such as those related to excessive exercise.