Physical activity regularly leads to a decline in lung function in children and adolescents with asthma. This decline is a consequence of what is known as exercise-induced asthma (EIA), and can be determined and graded with the help of lung function tests before and after submaximal workloads on the ergometer cycle or the treadmill. Typical EIA appears in asthmatic individuals with entirely normal lung function before the effort, but EIA may also become clinically manifest with exercise in patients who have a subclinical degree of obstruction. The grade of EIA is essentially dependent on the duration and intensity of effort but also on the type of exercise. For example, free running causes much greater bronchoconstriction than swimming. The temperature and humidity of the inspired air may partially explain this difference. At the Voksentoppen Allergy Institute we find that about 85% of children develop a fall in lung function of 15% or more after a six minute ergometer cycle test. With typical EIA the fall may be totally or partially abolished by prophylactic medication 10 minutes before the start of the test. Disodium cromoglycate (Intal) and/or beta-adrenergic drugs are regularly used before all physical activity. Training programmes must be based on the interval principle. Swimming, ball games, relay races and dancing are examples of useful activities in the training and rehabilitation of children and adolescents with asthma. Through prophylactic medication and physical training, the aerobic work capacity, muscle strength and lung function in asthmatic children is improved. Training also leads to a significant mobilisation of mental resources and an increase in social integration.