The incidence of respiratory allergy in an adult population from Lazio is reported. A high prevalence rate of bronchial asthma was found, whereas the evolution of allergic rhinitis into bronchial asthma was less pronounced than that reported for childhood allergy. The mean age of onset of the symptoms was 15 +/- 5 years. A remarkable number of patients suffered from oculorhinitis, which resulted in bronchial asthma in a mean time of 5 +/- 3 years. Most of the patients came from Rome and were low-middle class. Previous history of possible co-factors in the development of respiratory allergies showed a high percentage of family atopy and of asthmatiform bronchitis. Studies of allergens responsible for disease revealed that house mite dust and Dermatophagoides are the major allergens responsible for the symptoms. An analysis of the most common therapy used for treating patients demonstrated a prevalence of anti-histamine, DSCG and chetotifen whereas cortisone treatment and hospitalization were less overspread. The present epidemiological survey shows a prevalence of adult onset bronchial asthma due to house mite dust. The importance of this observation in preventive medicine programmes is discussed.