In 131 patients with chronic urticaria, including physical urticarias, oral provocation tests were done with aspirin. A total of thirty-one patients showed a reaction on aspirin challenge. Reactions were seen in 35% of patients with idiopathic urticaria, 52% of patients with cholinergic urticaria, and 43% of those with pressure urticaria. The patients with reactions to aspirin were also tested with tartrazine, sodium benzoate, 4-hydroxybenzoic acid, sodium- and phenyl salicylate and the analgesics indomethacin, paracetamol and mefanamic acid. In nineteen of twenty three aspirin sensitive patients, positive reactions to one or more of these substances were observed. Indomethacin and tartrazine had the highest scores. There was no statistically significant correlation between aspirin reactions and the presence of nasal polyposis, sinusitis, asthma or atopy.