We studied the effect of the weather on acute exacerbations of bronchial asthma in children by comparing records of 8,657 admissions for five acute respiratory diseases (3,064 for asthma) with concurrent meteorologic data. These diseases were classified according to their interrelations and distinct meteorologic patterns into two groups: (1) acute asthma and acute laryngitis, which are correlated with the afternoon gradients of air temperature, heat content (the thermal energy of the ambient air), and modified heat content factor (the energy required to heat the air water vapor to the ambient temperature), but not correlated with the absolute values of air temperature and water content: and (2), bronchopneumonia/pneumonia and upper respiratory infections, which are correlated only with the absolute values of the meteorologic parameters (air temperature, water content, heat content, and modified heat content factor), but not with their afternoon gradients. Admissions for bronchiolitis revealed an age-related pattern: up to 1 yr they resembled Group 2 and from 1 to 2 yr, Group 1. It follows that the admission rates of acute exacerbation of bronchial asthma in childhood are linked both to the afternoon weather gradients and to some of the acute respiratory infections.