The result of a study done on 52 subjects including a thorough ventilatory functional test and the radioisotopic measurement of inhaled particles deposition, by working out the TB/P ratio, revealed that: 1. giving aerosol needs an exacting technique when used for quantitative aims; 2. ratio TB/P is increased in patients with chronic broncho-pulmonary diseases, because of a predominantly tracheo-bronchial deposition of particles; 3. in patients with a satisfactory ventilatory function the TB/P ratio is increased; on the other hand in patients with ventilatory disorders, the ratio is normal. The repartition of particles deposition between the compartments TB and B depends therefore not only on factors involving ventilatory functional values but also on the physiopathological factors not included in them.