This randomised double-blind, placebo-controlled, cross-over study compared the effects of single oral doses of terfenadine 120 mg, cetirizine 10 mg, and loratadine 10 mg on experimentally induced weal and flare reactions. The areas of weal and flare induced by intracutaneous injections of histamine were measured using planimetry, weal thickness by A-scan pulsed ultrasound and erythema index by a device which measures the relative reflectance of red and green light. All three antihistamines suppressed the weal and flare area and weal thickness 3, 6, 12 and 24 h after dosing. At the usual currently recommended doses terfenadine and cetririzine were most effective after 6 h and were more potent than loratadine for the first 6 h of the study.