Oxybutynin has long been used for the treatment of patients with detrusor overactivity and urinary urge incontinence. The short half-life of oxybutynin administered as a conventional tablet formulation or syrup requires 2-3 times daily dosage to be effective. A new controlled release (CR) tablet for once-daily administration has been developed. The efficacy and tolerability of this new controlled release tablet was compared to that of a 5-mg conventional oxybutynin tablet administered twice daily. Seventeen female incontinent patients were studied in a double-dummy crossover trial. Efficacy and tolerability were assessed by using a voiding diary, pad-weighing test, visual-analogue scale (VAS), and questionnaire. Adverse events were recorded spontaneously on a questionnaire by the patients themselves throughout the study. Serum concentrations of oxybutynin and its active metabolite N-desethyloxybutynin were studied after both a single dose and multiple dosage. There was no difference in efficacy between the two formulations. Depending on the parameters tested, the change from baseline values in a positive direction ranged from 15 to 53%. The incidence of adverse events was similar with both formulations. Oxybutynin or its metabolite showed no cumulation during the multiple dosage with a 10-mg CR tablet. The controlled release tablet formulation is as effective and as well-tolerated as the conventional one, but has the advantage of only once-a-day dosage, enhancing treatment compliance.