BACKGROUND 　It is unknown whether inhaled corticosteroids can modify the subsequent development of asthma in preschool children at high risk for asthma．

METHODS 　We randomly assigned 285 participants two or three years of age with a positive asthma predictive index to treatment with fluticasone propionate (at a dose of 88 μg twice daily) or masked placebo for two years,followed by a one-year period without study medication．The primary outcome was the proportion of episode free days during the observation year．

RESULTS　 During the observation year．no significant differences were seen between the two groups in the proportion of episode-free days．the number of exac-erbations，or lung function．During the treatment period．as compared with placebo use．use of the inhaled corticosteroid was associated with a greater proportion of episode-free clays(P=0.006)and a lower rate of exacerbations(P<0.001)and of supplementary use of controller medication (P<0.001)．In the inhaled-corticos-teroid group．as compared with the placebo group．the mean increase in height was1.1 cm less at 24 months(P<0.001)，but by the end of the trial，the height increase was 0.7 cm less(P=0.008)．During treatment，the inhaled corticosteroid reduced symptoms and exacerbations but slowed growth，albeit temporarily and not progressively．

CONCLUSIONS　In preschool children at high risk for asthma．two years of inhaled-corticosteroid therapy did not change the development of asthma symptoms or lung function during a third．treatment-free year．These findings do not provide support for a subsequent disease modifying effect of inhaled corticosteroids after the treatment is discontinued．

(N Engl J Med 2006；354：1985-97.May 11,2006)