Geilomo hospital for children with asthma and allergy is situated 800 m above sea level in a non-polluted area in the central part of Norway. 31 children who were admitted to this hospital from different parts of Norway (mostly from the main cities) were studied for six weeks. They underwent physical training and daily measurements were taken of lung function and the effect of bronchodilators. The bronchial responsiveness of the children improved significantly from week 1 to week 6, as measured by reduction in lung function after sub-maximal running on a treadmill. There was significant improvement in daily symptom score, and in degree of obstruction as shown by physical examination. The children's improvement was probably the result of a stay in a mountainous area with very little air pollution or allergens, combined with regular planned physical activity, and regular medication and surveillance.