Astemizole, a new histamine H1 receptor antagonist, was tested in a double-blind cross-over comparison study with chlorpheniramine maleate, a very effective conventional H1 antagonist, in patients with chronic allergic rhinitis. Astemizole was found to be equally effective, yet there was a significant decrease in the side effects of sleepiness (P less than .01) and dry mouth (P less than .05). Astemizole has a completely different structure and binding curves from terfenadine. It is approved for clinical use in the United Kingdom, Canada, and many European countries.