The "vasoconstrictor" effect of dermally applicated steroids is a widely used parameter when determining the potency of glucocorticoids. A similar effect on the nasal mucosa has been suggested as providing an explanation for the clinical effect of topically administered glucocorticoids in the treatment of nasal disorders such as allergic and vasomotor rhinitis. The recently described 133Xe wash-out method was used for the purpose of blood flow determination in 11 healthy subjects. In a randomized double-blind cross-over study, the effect of topically administered budesonide, a non-halogenated glucocorticoid, for 1 week was compared with that of placebo. No difference was found to occur in the mucosal blood flow after the administration of budesonide, as compared with placebo. It seems likely that a more complex activity than vasoconstriction is responsible for the clinical effect in the treatment of nasal disorders, and further research is required in order to clarify this issue.