OBJECTIVE To investigate the effects of alpha1 adrenoceptor antagonist doxazosin on the growth of androgen-independent prostate cancer cell PC-3 transplanted in nude mice. METHODS PC-3 cells xenografts were transplanted (s.c.) in nude mice, and thirty xenografts were established successively. They were then randomly divided into 5 groups: A (control group), B (doxazosin 3 mg/kg), C (doxazosin 10 mg/kg), D (doxazosin 30 mg/kg), and E (doxazosin 100 mg/kg). Seven days after implantation, doxazosin was administered in sterile water by oral gavage, and the volumes of the transplanted tumors were measured during the therapy twice a week. All the mice were sacrificed after two weeks of doxazosin administration; the tumors were resected to do the following research. Immunohistochemistry of Ki67 and terminal deoxynucleotidyl transferase-mediated dUTP biotin nick end labeling (TUNEL) was done to study the effects of doxazosin on the proliferation and apoptosis of prostate cancer cells; moreover, we also used Western blotting to study the protein expression of Smad-4 and IkappaB alpha. RESULTS Nude mouse experiments showed that the in vivo doxazosin administration induced a notable decrease in the volumes of prostate cancer xenografts compared with the control group, and the tumor weights were also decreased. Interestingly enough, administration of doxazosin at higher concentrations (10, 30, 100 mg/kg) did not have further effect on tumor suppression. The percentage of PC-3 TUNEL positive cells was significantly higher than that of the control group; while the doxazosin treated groups and the control group did not have statistical difference on the percentage of Ki67 positive cells. In doxazosin treated groups Smad-4 and IkappaB alpha expressions were higher than that of the control group. CONCLUSIONS Doxazosin can inhibit the growth of the prostate xenografts in the nude mice by inducing apoptosis without affecting the cell proliferation. Activation of transforming growth factor beta1 (TGF-beta1) signaling pathway may be the mechanism underlying doxazosin-mediated apoptosis.