The clinical findings, allergoimmunological results and lung function data of 208 asthmatic children (aged 4-18 years), admitted to the Pediatric Outpatient Department were investigated. In respect to the case history and the clinical findings the patients were divided into 5 etiopathogenetic groups including infectious asthma (6%), seasonal asthma (29%), exogenous perennial asthma (56%), intrinsic asthma (4%) and exercise-induced asthma (5%). All patients presented with increased airway resistance measured plethysmographically (Raw greater than 120% predicted) as indicator of bronchial hyperreactivity. On a functional basis patients with perennial asthma were subdivided into those with predominant hyperinflation (thoracic gas volume, TGV greater than 120% predicted), those with hyperinflation and airway obstruction (Raw greater than 120%), and those with airway obstruction without overinflation. By the method of circular statistics the influence of salbutamol, a beta-2-mimetic drug inhaled by pressurized aerosol, was studied to evaluate the reversibility of these functional abnormalities in the symptom free interval of disease. Response to therapy was best in the group with predominant airway obstruction without hyperinflation. In contrast, patients with airway obstruction and/or hyperinflation showed only partial reversibility of pathophysiological alterations. Hyperinflation usually causes only minor clinical symptoms but leads to the development of irreversible lung damage in the form of "loss of elastic recoil". Therefore, it is suggested that early diagnosis and strict medical management are mandatory in patients with hyperinflation.