We examined the correlation between the expression of α 1 -adrenoceptor subtype mRNA in the prostate and the clinical efficacy of subtype selective α 1 -adrenoceptor antagonists. We discuss the possibility of individualizing drug therapy in patients with benign prostatic hyperplasia.A total of 33 patients randomized to the tamsulosin group and 28 randomized to the naftopidil group were enrolled in this study. Each group of patients was administered 0.2 mg tamsulosin hydrochloride or 50 mg naftopidil daily for 12 weeks. Four prostate needle biopsy specimens were obtained from the transition zone to examine the expression of α-adrenoceptor subtypes. Specimens were stored at –80C until used for TaqMan® quantitative reverse transcriptase-polymerase chain reaction, which was performed after 12 weeks of treatment.Based on the results of quantitative reverse transcriptase-polymerase chain reaction the tamsulosin and naftopidil groups were grouped into α 1a -adrenoceptor dominant (22 and 12 patients) and α 1d -adrenoceptor dominant (11 and 16, respectively) subgroups. The efficacy of tamsulosin hydrochloride and naftopidil differed depending on the dominant expression of the α 1 -adrenoceptor subtype in the prostate. Tamsulosin hydrochloride was more effective in patients with dominant expression of the α 1a -adrenoceptor subtype, whereas naftopidil was more effective in those with dominant expression of the α 1d -adrenoceptor subtype.The expression level of α 1 -adrenoceptor subtype mRNA in the prostate could be a predictor of the efficacy of subtype selective α 1 -adrenoceptor antagonists in patients with benign prostatic hyperplasia. This result implies that genetic differences are responsible for the diverse responses to these drugs.