Ketotifen 1 mg b.d. (oral) and sodium cromoglycate 20 mg q.i.d. (inhalation) were compared in a double-blind crossover trial in 43 asthmatic outpatients. Comparison of diary card scores and pulmonary function tests showed significant improvement over a 12 week period on each drug. Comparison of the diary card scores and pulmonary function tests showed no significant difference between the drugs after 12 weeks of treatment. Twenty-six patients experienced sedation and/or lethargy whilst on ketotifen and 11 patients had similar side effects whilst on cromoglycate. Physician preferences based on diary card and pulmonary function data showed an approximately equal number of preferences for each medication and also a small group of patients in which no preference could be made. The present trial suggests that both ketotifen and cromoglycate are effective in the management of outpatient asthma. When all the patients are considered as a group no distinction can be made between the two drugs; on the basis of physician assessment of each patient, it appears that some patients may do better on ketotifen and others on cromoglycate.