Objectives. To evaluate the efficacy and tolerability of a new extended-release (ER), once-daily, capsule formulation of tolterodine, relative to placebo and the existing immediate-release (IR), twice-daily, tablet formulation, for treatment of the overactive bladder. Methods. This was a double-blind, multicenter, randomized, placebo-controlled trial. One thousand five hundred twenty-nine patients (81% women) with urinary frequency (eight or more micturitions every 24 hours) and urge incontinence (five or more episodes per week) were randomized to oral therapy with tolterodine ER 4 mg once daily (n = 507), tolterodine IR 2 mg twice daily (n = 514), or placebo (n = 508) for 12 weeks.