A double-blind placebo-controlled trial was carried out to assess the efficacy of ketotifen in the pre-school asthmatic. The trial period consisted of a 1-month run-in period followed by a 4-month treatment period. Symptom scores for asthma, rhinitis, eczema and, where possible, twice daily peak flow measurements (24 cases) were recorded on diary cards by the parents. All concomitant medication used in addition to the trial drug was noted. The only medication not allowed was disodium cromoglycate. A total of 37 children, 23 boys and 14 girls, mean age 4.1 years (range 1.3-5.9 years) completed the trial. They comprised 19 given ketotifen and 18 given placebo. All were atopic and had allergic rhinitis and 15 had eczema. Ketotifen dosage was 1 mg twice daily in the under 5-year-olds (23 cases) and 2 mg twice daily in the remainder. On analysing the results no significant benefit could be demonstrated for giving ketotifen in this group of patients.