A group of forty-two steroid-dependent perennial asthmatics was studied over a 13-week period including the 8 weeks of a double-blind controlled trial of oral sodium cromoglycate. Given at a dose of 200 mg four times per day the drug provided no significant benefit to the patients when compared with results for those on placebo. Blood from eleven patients consistently failed to release more than 25% of the total cellular histamine when challenged with a range of concentrations of antibody to IgE. All six of the cryptogenic (intrinsic) asthmatics in the trial fell within this group, together with 2/12 asthmatics with negative skin tests but suggestive clinical histories implicating common allergens, and 3/24 extrinsic asthmatics with positive skin prick tests. There was no correlation between drug usage and histamine release in response to challenge with antibody to IgE.