In adults with asthma, heterogeneity in response to montelukast is associated with a polymorphism in the ALOX5 promoter.14, 15 In line with these studies in adults, we recorded a 20% reduction in unscheduled medical attendances for wheeze in children in the montelukast group with the 5/5 ALOX5 promoter genotype, and no effect of intermittent montelukast in those with the 5/x+x/x genotype. Here, ALOX5 is linked to asthma.