1. Mizolastine, a new benzimidazole derivative with potent selective, non-sedative H1-histamine antagonist activity was compared with terfenadine, cetirizine and loratadine using the histamine-induced wheal and flare model in healthy volunteers. 2. Study design was a five way double-blind crossover design using a single dose of mizolastine 10 mg, terfenadine 120 mg, cetirizine 10 mg, loratadine 10 mg and placebo. 3. Histamine tests were performed on 10 occasions up to +24 h after dosing using an intradermal injection of histamine 2 micrograms with concommittant contralateral injection of a saline control. 4. Mizolastine, terfenadine, cetirizine and loratadine significantly (P < 0.001 vs placebo) inhibited the wheal and flare formation starting 1 to 2 h after dosing up to 24 h after dosing. 5. Mizolastine was significantly more active than loratadine on the wheal (P < 0.01) and flare (P < 0.05) inhibition from 3 up to 6 and 8 h respectively, as active as terfenadine on both parameters and as active as cetirizine on wheal inhibition while less active (P < 0.01) than cetirizine on flare inhibition at 2 and 12 h post-dosing.