['To determine the effect of 1,25(OH)(2)D(3) and 25(OH)D(3) vitamin D derivates on the growth of leiomyoma and myometrial cells in vitro.', 'In vitro study.', 'Cell biology research laboratory.', 'Six premenopausal women with uterine leiomyomas undergoing hysterectomy.', 'Samples of leiomyomas and normal myometrial tissue were obtained, and paired cultures were established.', 'A colorimetric crystal violet assay to determine the effect of 1,25(OH)(2)D(3) and 25(OH)D(3) on cell growth.', 'In both myometrial and leiomyoma cells, 0.1 nM physiologic level of 1,25(OH)(2)D(3) inhibited growth by 12% when compared with controls. The growth inhibition was concentration dependent; the highest concentration of 1,25(OH)(2)D(3) (100 nM) inhibited growth by 62% in both cell types. All the differences were statistically significant. A slight stimulation (<4%) of cell proliferation was observed with the lowest 25(OH)(2)D(3) concentrations. When treated with either a 500 nM or 1000 nM concentration of the compound, the growth of both cell types fell to approximately 50% of that of the control cultures, and the level of inhibition with the latter concentration was statistically significant.'] Does vitamin D inhibit myometrial and leiomyoma cell proliferation in vitro?