The HI-antihistamine chlorpheniramine and the H2-antihistamine cimetidine, given alone and in combination, have been compared with placebo in twenty patients with factitious urticaria (dermographism), in a double-blind, randomized cross-over trial. Of these regimes, the combination was the only treatment which significantly reduced weal size, flare size and duration of weal, compared with placebo, although other treatments approached statistical significance. Continuation of the most effective of the four treatments in nineteen of the patients for a further 3 months without breaking the randomization code provided further evidence of the great effectivness of combined cimetidine and chlorpheniramine. No significant side effects were note.