Eleven boys with bronchial asthma, mean age 11.2 years, particpated in a 20-month long physical activity programme. The training was performed in an ordinary indoor gymnasium for one hour twice a week. No drugs were given prior to the training sessions. Cardiorespiratory function and dimensions and maximal aerobic capacity were determined before, during and after the training period. The respiratory and circulatory dimensions increased as expected during and after the training period. The respiratory and circulatory dimensions increased as expected during the observation period and after correction for the influence of growth no changes were seen in the variables studied. Nor did the training group differ significantly in any respect from a group of nine asthmatic boys not trained. There was only a slight but not significant increase in the maximal exygen uptake and the ventilatory coefficient in the training group as compared to the non training group. After a one-week winter-camp with high exercise intensity there was a rise in the total ventilation, the ventilatory coefficient and the maximal work performed but the maximal oxygen uptake was not affected. All boys showed a very good ability to participate in the physical activity programme at approximately the same level as the physical education given at school.