Uterine leiomyomas (fibroids) are the most common benign tumors in women of reproductive age. Although the local application of low doses of methotrexate (MTX) is used as an effective treatment of the myomas, myotrexate could be a promising new drug. This study investigated the cytotoxic and apoptotic effects of both MTX and myotrexate in human fibroblasts derived from the uterine fibroids (T hES cell line). The myotrexate adduct is an aqueous solution of MTX and L-arginine. Cells were treated with a graded concentrations of both MTX and myothrexate (0.1-16 µM) for 24 h. The cytotoxicity was assayed by MTT test, apoptosis was evaluated by Annexin V-FITC assay and their possible role in apoptosis was determined by immnu- flourescence. Both MTX and myotrexate induced apoptosis in T hES cells in a dose dependent manner (p < 0.001). Myotrexate significantly increased the percentage of AnnexinV positive cells, BAX/Bcl-2 ratio and subsequent caspase-3 activation compared to the MTX treated cells (p < 0.05). Both MTX or myotrexate treatment showed a diffuse staining of cytochrome c indicating its release from mitochondria to the cytosol, suggesting that their mechanisms of action most likely involves the mitochondrial apoptotic pathway.