The responsiveness to bronchodilator is variable in infants with wheezing associated respiratory illness (WARI). Factors for prediction of the response will lead to more rational use of the bronchodilator in these infants. We examined the possible predictive factors in 44 children under 2 years of age who had their first episode of WARI. All of them were treated with 0.15 mg/kg of nebulized salbutamol. Thirty patients (68%) with decreasing clinical score > or = 3 after treatment were considered as the responders while the remainder (14 infants) were non responders. By using Chi-square test, Fisher exact test and Mann-Whitney U test to compare the data of the 2 groups, the significant factors for the responders were older than 6 months and history of previous LRI (p < 0.01). The significant factors for the non-responders included concurrent diarrhea, patchy pulmonary infiltration and positive RSV in the nasopharyngeal secretion (p < 0.01). These results suggested effective bronchodilator therapy in infants older than 6 months or having a history of previous LRI. Those who had acute RSV infection or patchy infiltration in chest X-ray and associated diarrhea were less likely to respond.