Detrusor instability occurs in approximately 10% of the adult population, producing troublesome symptoms. The pharmacotherapy currently available is usually only partially effective and cannot be adequately evaluated except under "blind" conditions because of the significant component attributable to placebo effects. The results of the present study revealed no advantage resulting from treatment with flavoxate, as assessed both subjectively and objectively. We suggest that this therapy does not appear to be beneficial in the medical management of detrusor instability.