Upper respiratory infections (URI) during the first years of life are mostly viral in origin. However, a number of observations suggest the influence of both predisposing and triggering factors. Atopy in particular seems to play an important role as do environmental factors. Many children with early symptoms such as blocked or runny nose are likely to become skin-positive later in life to antigens such as, e.g., D. pteronissinus. A standardized questionnaire was administered to 2304 schoolchildren in order to ascertain the URI frequency and to correlate it with family and environmental factors and with results of prick tests for main allergens in our climate (D. pteronissinus and Grasses). Results showed a wide overlapping of URI and lower respiratory illnesses (in particular, asthma), which are widely distributed in the families of patients. Passive smoking and the quality of housing are the main triggering environmental factors. In our sample, skin positivity for D. pteronissinus and Grasses largely exceeds the symptomatic portion of the whole population. It is therefore suggested that many asymptomatic children are "at risk" for allergic respiratory illness. The highest incidence of winter rhinitis in skin-negative subjects (71.7%) and the skin positivity for D. pteronissinus in patients with perennial symptoms, suggest the importance of both atopy and viral infections in the occurrence of URI. Nasal troubles are most frequent in asthmatic subjects and may be considered the actual additional symptom in asthma.