In a prospective study the effects of the anticholinergic drugs oxyphenonium bromide and oxybutynin hydrochloride on detrusor contractility and reflux were studied. Although anticholinergic properties are claimed of both drugs, only oxybutynin hydrochloride proved to decrease detrusor contractility and the degree of reflux, probably due to a direct spasmolytic effect on the detrusor. Therefore, in cases of reflux and detrusor instability treatment with oxybutynin hydrochloride is recommended.