Eleven patients with primary acquired cold-induced urticaria were treated with ketotifen (1 mg b.i.d.) or placebo in a double-blind, crossover design trial. After seven days of ketotifen treatment, reaction times to a cold stimulus were significantly delayed in ten of the 11 subjects. No effect was seen after placebo treatment. It is concluded that ketotifen may have a place in the treatment of primary acquired cold urticaria.