Combination Treatment With Doxazosin Plus TolterodineSR 2 mg Versus 4mg in Men With an Overactive Bladder (OAB) and Benign Prostatic Hyperplasia (BPH)

Inclusion Criteria: * Male aged 50 ≤ and ≤ 80 years * Proven bladder outlet obstruction (BOO, Abrams/Griffith score \>20) on urodynamic study * Symptoms of OAB as verified by the 3 day voiding diary, defined by: 1. symptoms of urinary urgency (defined as a level of ≥3 in a 5 point urgency scale) at least two episode per 24 hours and 2. symptoms of urinary frequency (8 micturitions per 24 hours) * Total International Prostate Symptom Score (IPSS) of 12 or higher * IPSS quality-of-life (QOL) item score of 3 or higher * A rating of the bladder condition at Baseline prior to randomization as "Some Moderate Problems", "Severe Problems", or "Many Severe Problems" on the Patient Perception of Bladder Condition (PPBC) questionnaire. * Ability and willingness to correctly complete the micturition diary and questionnaire * Capable of understanding and having signed the informed consent form after full discussion of the research nature of the treatment and its risks and benefits Exclusion Criteria: * Patients have a baseline post-void residual (PVR) which exceeded 150 mL. * Any condition that is a contraindication for anticholinergic treatment, including uncontrolled narrow-angled glaucoma, urinary retention or gastric retention. * Symptomatic acute urinary tract infection (UTI) during the screening period. * Treatment within the 14 days preceding randomization, or expected to initiate treatment during the study with any anticholinergic drugs and drug treatment for overactive bladder. * A 5-alpha reductase inhibitor if started less than 3 months prior to screening. * Patients with previous urethral, prostate or bladder neck surgery. * Patients with cancer of any type including cancer of the prostate or bladder, uncontrolled medical condition including psychiatric disease or life threatening illness. * Patients with Parkinson's disease, stroke, multiple sclerosis, spinal cord disease. * Patients with suspected neurogenic bladder disorder. * Patients with urethral stricture or bladder neck contracture. * Serum PSA 4ng/ml (only patients with no malignancy by prostate biopsy can be included).