In a double-blind, placebo-controlled study control of asthma was assessed by diary symptom cards, peak-flow measurements and lung function within 3 treatment groups over a 6 months period. 36 children (25 boys, 11 girls 5.5 to 13.2 years of age) with exogen allergic, perennial asthma inhaled either beclomethasone dipropionate (BDP) with salbutamol (S) or disodium cromoglycate (DNCG) with S or a placebo preparation with S from metered dose inhalers (MDI) through a large-spaced auxiliary device (Volumatic). At entry, after 2 and 4 months lung function tests were performed evaluating changes in the degree of pulmonary hyperinflation, bronchial obstruction, and bronchial hyperreactivity (BHR). Daily PF measurements showing wide variations (up to 10-12%) were insensitive to indicate any significant changes. In contrast evaluation of symptom diaries presented dramatic improvement during the first 3 months of the study. In addition, the DNCG group showed significant improvement of BHR (p = 0.02). Moreover, the majority of patients on regular therapy with salbutamol and placebo showed an increase of airway resistance. It is concluded that even in mild childhood asthma, for optimal control a combination of a beta 2-stimulant as bronchodilator and DNCG or BDP as protector should be applied.