This study was conducted to elucidate the effects of raloxifene on proliferation and apoptosis in cultured human uterine leiomyoma cells. The monolayer cultures were treated with graded concentrations (10(-9), 10(-8) and 10(-7) M) of raloxifene and 10(-7) M 17beta-estradiol (E(2)). Cell viability, percentage of proliferating cell nuclear antigen (PCNA)-positive cells, percentage of terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate nick-end labelling (TUNEL)-positive cells and the expression of PCNA and Bcl-2 proteins were assessed by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxylphenyl)-2-(4-sulphophenyl)-2H-tetraz olium assay, immunocytochemistry, TUNEL assay and western blot analysis, respectively. Compared with untreated cultures, the number of viable cultured cells, percentage of PCNA-positive cells and PCNA protein expression were significantly decreased by treatment with 10(-9) M raloxifene, but increased by treatment with either 10(-8) M or 10(-7) M raloxifene. In contrast, the percentage of TUNEL-positive cells was significantly increased and Bcl-2 protein expression was significantly decreased by treatment with 10(-9) M raloxifene, whereas they were not affected by treatment with either 10(-8) or 10(-7) M raloxifene. In cultured leiomyoma cells, low concentration (10(-9) M) of raloxifene may inhibit the growth of leiomyoma cells, whereas high concentrations (10(-8) M, 10(-7) M) of raloxifene may promote their growth.