Tamsulosin has higher selectivity for the pharmacological a1-adrenoceptor subtype and the cloned a1a subtype than for the a1b subtype. Tamsulosin 0.4 mg improved Qmax to a slightly greater extent than alfuzosin 10 mg.(26% and 16% versus baseline, respectively)(http://www. fda.gov/cder/approval/ index.htm;accessed October 27, 2003.) and Tamsulosin 0.4 mg o.d. has been reported to be well tolerated irrespective of age and/or cardiovascular comorbidity/co-medication (Michel et al 1998) and no interaction with several antihypertensive agents has been reported. (Lowe et al. 1997) Our study is to explore the efficacy and safety of tamsulosin 0.4mg (Harnal® D. 0.2mg, 2T) in patients with LUTS/BPH refractory to tamsulosin 0.2mg (Harnal® D 0.2mg, 1T).