The present study was conducted to evaluate the effects of the progesterone receptor modulator CDB-2914 on proliferative activity and apoptosis in cultured human uterine leiomyoma cells. Isolated leiomyoma cells were subcultured in phenol red-free DMEM supplemented with 10% fetal bovine serum for 120 h and then stepped down to serum-free conditions for 12, 24, 48, and 96 h in the absence or presence of graded concentrations of CDB-2914 (10(-9), 10(-8), 10(-7), and 10(-6) M). The number of viable cultured leiomyoma cells was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazodium bromide assay. Proliferating cell nuclear antigen (PCNA) expression was evaluated by immunocytochemistry and Western blot analysis. Apoptosis was examined by terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate nick end labeling (TUNEL) assay. Caspase-3, cleaved poly(ADP-ribose) polymerase (PARP), and Bcl-2 expression were assessed by Western blot analysis. Compared with untreated control cultures, treatment with CDB-2914 decreased the number of viable cultured leiomyoma cells and the PCNA-positive rate in those cells and increased the TUNEL-positive rate in cultured leiomyoma cells in a dose-dependent manner. Western blot analysis revealed that treatment with CDB-2914 significantly decreased the expression of PCNA and Bcl-2 protein and increased the expression of cleaved caspase-3 and cleaved PARP in a dose-dependent manner compared with untreated control cultures. These results suggest that CDB-2914 inhibits the proliferation of cultured leiomyoma cells by down-regulating PCNA expression and induces apoptosis by up-regulating cleaved caspase-3 and PARP expression and down-regulating Bcl-2 protein expression in those cells.