The effects of sodium cromoglycate and ketotifen were studied in a group of 20 patients in whom fish repeatedly provoked an attack of wheezing and dyspnoea within one hour of its being eaten. Fish ingestion resulted in a fall in forced expiratory volume in one second (FEV1) of at least 15%. All patients had a weal greater than 4 mm in response to fish antigen in the skinprick test and most had blood eosinophilia and raised serum IgE levels. Administration of drugs and placebos was carried out under double-blind conditions, in a randomised fashion, on different days. Cromoglycate blocked the fall in FEV1 either completely or significantly in 16 patients. Ketotifen did not appear to have any significant effect in the group as a whole.