Ten boys 9-12 years of age with severe perennial asthma participated in a physical exercise programme lasting 8 months. Pulmonary function and psychological tests were performed before training, immediately after, and one year after the end of the exercise programme. Static lung volumes, flow-volume variables and histamine tolerance were used as indicators of pulmonary function. Ego structure, body image, social development and concentration capacity were used as indicators of personality development. Before the study, the group had high FRC (p less than 0.05) and RV (p less than 0.001), low FEV1, MEF50 and MEF25 (all p less than 0.001) and low histamine tolerance. They showed marked disturbances in their personality development with low scores in psychological variables. During the training period, MEF50 and MEF25 increased slightly (p less than 0.01). Marked improvement was observed in all psychological variables (p less than 0.001). The positive effects remained during the following year. The marked and lasting improvement in personality development was regarded as an essential factor behind the more modest positive clinical and pulmonary function changes. The results emphasize the importance of including exercise programmes in the treatment of children with asthma.