Oxymetazoline, a derivative of imidazoline, is a widely used nasal decongestant. In contrast to other topical decongestants related to phenylephrine, sympathomimetic amines, it also induces a reduced nasal mucosal blood flow. The purpose of the present investigation was to evaluate the duration of effect of oxymetazoline on nasal airway resistance and mucosal blood flow. During the eight hours of study, the blood flow was reduced by 30-40 per cent in six hours. A similar decongestant effect of about 30 per cent was found during the same interval. The pharmacological profile of oxymetazoline seems questionable, since a reduced nasal mucosal blood flow might not be of value in the treatment of upper airways infections.