Terfenadine is a selective H1-histamine receptor antagonist. The lack of significant terfenadine penetration into the CNS is probably responsible for its lack of CNS effects. Terfenadine neither impairs psychomotor performance nor adversely affects subjective feelings, nor enhances the depressant effects of concomitantly administered alcohol or benzodiazepines. In controlled studies, the incidence of sedation due to terfenadine was comparable with that of placebo and significantly less than that with conventional antihistamines. Clinical studies have shown terfenadine to be comparable in efficacy with other antihistamines while being superior to placebo in alleviating the symptoms of seasonal allergic rhinitis. Additionally, there is good evidence that it is similarly as effective when used in the treatment of perennial rhinitis and histamine-mediated skin diseases. Thus, terfenadine offers a worthwhile improvement in side effect profile over 'traditional' antihistamines, and could well become an 'agent of choice' (along with other non-sedating antihistamines) in many patients in whom a histamine H1-receptor antagonist is indicated.