Tolterodine is a potent antimuscarinic agent specifically developed for the treatment of urinary urge incontinence and other symptoms related to the overactive bladder. In order to assess the optimum dosage for use in future clinical studies, a double-blind, randomized, placebo-controlled, parallel-group, multicenter study was performed in 90 patients with detrusor hyperreflexia and symptoms of urinary urgency, frequency, and/or urge incontinence. Urodynamic variables, micturition diary variables, and subjective urinary symptoms were measured before and after 2 weeks' treatment with either placebo or tolterodine 0.5, 1, 2, or 4 mg twice daily (bd). Serum drug concentrations, electrocardiogram recordings, blood pressure, and incidence of adverse events were also assessed. Linear regression analysis showed a significant dose-response relationship for several clinically relevant urodynamic variables, while there was a trend towards an improvement in micturition diary variables and subjective assessment of symptoms with increasing dosages of tolterodine. There were no safety or tolerability concerns regarding any of the dosages of tolterodine investigated, although 2 patients treated with a dosage of 4 mg bd experienced urinary retention that necessitated dosage reduction. The results of this study suggest that tolterodine is well-tolerated and exerts a dose-dependent effect on bladder function in patients with detrusor hyperreflexia. The optimum dosage of tolterodine for use in future studies is 1-2 mg bd.