Respiratory syncytial virus (RSV) bronchiolitis in infancy can lead to bronchial hyper-reactivity or recurrent obstructive bronchitis. The aim of the present study was to determine whether the type of treatment has an influence on respiratory status after RSV bronchiolitis. The study involved 117 infants (mean age 2.6 months), who needed hospital treatment because of RSV bronchiolitis. The patients were divided randomly into three groups. All received the same symptomatic treatment. Group I children received symptomatic treatment only, group II children were treated for 7 days with inhaled budesonide, 500 microg three times per day, administered via a nebulizer. Group III children received nebulized budesonide, 500 microg twice per day for two months. Follow-up consisted of out-patient check-ups 2 and 6 months after the infection, and telephone contact two years after the infection. Statistically significant differences were seen between the groups. In group I 37% of the children had asthma, in group II 18%, and in group III 12%. According to the present study it seems that inhaled corticosteroid treatment during and after the acute phase of infant RSV bronchiolitis may have a beneficial effect on subsequent bronchial wheezing tendency.