The effect of exogenous 1,25(OH)2 vitamin D3 (1,25(OH)2D3) on the CD3+, CD4+ and CD8+ subsets (counts/ul) of T lymphocytes was investigated in two randomized groups of postmenopausal women. Group one (16 subjects) received 1 ug/day of the secosteroid for 14 days, while group two (14 participants) was treated with 2 ug/day for the same period. The placebo group comprised another 10 postmenopausal women. Compliance of the treatment was controlled by serum intact parathyroid hormone (PTH) levels, which markedly declined at the end of the treatment (p<0.01 for both doses). The vitamin D status of the women before the treatment was defined by serum 25(OH) vitamin D (25(OH)D) levels. The lower dose of the secosteroid did not change any of the measured immune parameters. After a higher dose of 1,25(OH)2D3 the mean values of CD3+ and CD8+ increased (p<0.05 for the both parameters), but no changes in total lymphocytes and the CD4+ subset were observed. There were no correlations between the immune response (delta CD3+, delta CD4+ and delta CD8+) and basal circulating 25(OH)D. Briefly, then, 1,25(OH)2D3 slightly but significantly increases CD3+ and CD8+ subsets independently on the initial vitamin D status of the postmenopausal women.