['To determine if the use of the whistle watch (WW), a simple device to monitor peak flow rate, affects the use of bronchodilators at home.', 'Prospective, randomised, crossover design.', "The asthma outpatients' clinic at Coronation Hospital, a tertiary care centre in Johannesburg.", "Children between 6 and 18 years of age with moderate or severe asthma for more than a year were enrolled. They were randomised into two groups, with bronchodilator use determined either by the WW or solely by the patient's perceived symptomatology. The patients acted as their own controls, switching over to the other group after 30 days. Eighty patients were enrolled into the study.", 'Forty-three patients completed the study (54%). There were no significant differences between these patients and those who did not complete the study in terms of sex, age and treatment characteristics. There was a significant reduction in the mean monthly number of bronchodilator doses used by the WW group (5.5 doses v. 16.81 doses, paired t-test, t = 3.64, P < 0.001, 95% confidence interval (CI) 6.1-16.55). The change in individual participants varied between 13 extra bronchodilator doses and 71 fewer doses per month with the use of the WW device.'] Do effect of the whistle watch device on bronchodilator use in children with asthma?