Fifteen patients were included in a double-blind cross-over trial to investigate the efficacy of oral sodium cromoglycate in the treatment of chronic urticaria. Only patients with positive oral provocation tests were entered into the study. The challenging agents were food additives or antirheumatic agents. Treatments were taken for 4 weeks and the dose of sodium cromoglycate was 200 mg four times daily. No significant differences were found between active and placebo treatment periods for diary card symptom scores. Six patients preferred the active treatment, two preferred placebo and seven had no preference. The clinician showed no preference for either treatment.