OBJECTIVES:Some studies suggest that bioavailable 25-(OH)D is more accurate than total 25-(OH)D as an assessment of vitamin D status in black individuals, We hypothesized that increases in bioavailable 25-(OH)D would correlate better with improvement in bone outcomes among black HIV-infected adults. DESIGN:This is a secondary analysis of ACTG A5280, a randomized, double-blind study of Vitamin D3 and calcium (VitD/Ca) supplementation in HIV-infected participants initiating antiretroviral therapy (ART). METHODS:Effect of VitD/Ca on total and calculated bioavailable 25-(OH)D, parathyroid hormone (PTH), bone turnover markers (BTMs) and bone mineral density (BMD) in black and non-black participants were evaluated at 48 weeks. Wilcoxon signed-rank tests and Wilcoxon rank sum tests assessed within and between-race differences. RESULTS:Of 165 participants enrolled, 129 (40 black and 89 non-black) had complete data. At baseline, black participants had lower total 25-(OH)D median (Q1,Q3) 22.6 (15.8, 26.9) vs. 31.1 (23.1, 38.8) ng/ml, p < 0.001 but higher bioavailable 25-(OH)D 2.9 (1.5, 5.2) vs. 2.0 (1.5, 3.0) ng/ml, p=0.022 than non-black participants. After 48 weeks of VitD/Ca supplementation, bioavailable 25-(OH)D increased more in black than non-black participants, but there were no between-race differences in change in BTMs or BMD. The associations between increases in 25-(OH)D levels and change in bone outcomes appeared similar for both total and bioavailable 25-(OH)D. CONCLUSIONS:Baseline and change in bioavailable 25-(OH)D were higher among black adults initiating ART with VitD/Ca; however, associations between 25-(OH)D and bone outcomes appeared similar for total and bioavailable 25-(OH)D. The assessment of total 25-(OH)D may be sufficient for evaluation of vitamin D status in black HIV-infected individuals.