Nitroxazepine is a tricyclic antidepressant (TCA) for the treatment of depression. Nitroxazepine acts as a serotonin-norepinephrine reuptake inhibitor. The in vitro effect of Nitroxazepine (Sintamil), as a modulator alone and in combination with hydroxyurea (HU), on cytotoxicity is studied in 16 cases of human chronic myeloid leukemia (CML). The cytotoxicity of the drugs as a function of the exposure dose (HU, 100 μM; Nitroxazepine, 10 μg/mL) and the exposure time (1 h) to the agent is investigated. Cytotoxicity is evaluated as the inhibition of incorporation of [3H-methyl]thymidine in the nucleic acids of CML cells. Cytotoxicity of HU is greatly enhanced (P<0.001) by 1 h exposure of the CML cells to Nitroxazepine. The present data indicate that Nitroxazepine potentiates the cytotoxic activity of HU in CML cells. Nitroxazepine is indicated for the treatment of nocturnal enuresis. Nitroxazepine has similar effects to imipramine, but with certain advantages, such as lower anticholinergic side effects.