The efficacy of Ketotifen was examined in the treatment of 113 infants between 6 and 36 months of age presenting with a history of cough and/or wheeze in a multicentre randomized placebo-controlled double-blind study. A 4 week no-medication baseline phase preceded the 16 week treatment phase in which infants took 2.5 mL twice daily of either placebo or Ketotifen (0.5 mg) syrup; this was followed by a 4 week wash-out phase. Diary card evaluation was performed by the parent or guardian for the duration of the study and recorded wheeze and cough twice daily as well as medication used. The percentage of symptom-free days decreased significantly in both groups (P < 0.005) with placebo-treated infants experiencing significantly more symptom-free days compared with the Ketotifen group (P < 0.01), although this difference was never more than 10% in any 4 week treatment period. Symptom severity scores and use of beta-agonist medication were also less in the placebo-treated infants but did not reach statistical significance. This study was unable to show a therapeutic advantage of Ketotifen over placebo in this group of infants with chronic cough and/or wheeze and the apparent statistical advantage of placebo is not a clinically relevant finding.