In this study, the potential for short courses of glucocorticoids to prevent or reduce the severity of asthma induced by viral respiratory infections in preschool children was investigated. Two groups of children with a mean age of 36.4 +/- 3.9 months and 40.4 +/- 4.9 months were monitored during a 2-year period. Group 1, considered as the control group, received theophylline preparations and orciprenaline either on a continuous basis or during attacks. During severe attacks, albuterol was administered by nebulization, with corticosteroids occasionally added for seven to 14 days in cases of poor response to albuterol. Group 2 received the same treatment during the first year. During the second year, however, a short-term course of prednisone (1 mg/kg) was given as soon as the first symptoms of an upper respiratory tract infection appeared, prior to any signs of wheezing. Results indicate that, whereas morbidity remained constant in the control group during the 2-year observation period, a significant decrease in the number of wheezing days (65%), attacks (56%), visits to the emergency room (61%), and hospitalizations (90%) occurred in group 2. It was concluded that preschool children who suffer from repeated asthma attacks related to upper respiratory tract infections may benefit greatly from the preventive administration of corticosteroids.