Fifty children with exercise-induced asthma (EIA) volunteered to take part in a study of the influence of training on EIA. 1) Ten children did not change physical activity. 2) Twelve children trained after premedication with salbutamol inhalations. 3) Thirteen children trained after premedication with disodium chromoglicate (DSCG) and used that drug for treatment. 4) Fifteen children trained in their own regimen, commonly after premedication with salbutamol. Their training programme (groups 2-3) consisted of high load exercise periods of two minutes interrupted by intervals of rest for two minutes during 30 minutes followed by interval swimming for another 30 minutes, twice a week for 3-4 months. Before the training period the degree of EIA was tested with a battery of lung function tests before and after running for 6 minutes on a treadmill at heart rate 170. EIA after training was measured applying the same procedure. Cardiocirculatory performance was evaluated before and after training with work on a cycle ergometer and expressed as W/kg body weight at heart rate 170. The children in groups 2, 3 and 4 improved their physical working capacity by 11% (p less than 0.01), 21% and 11%, respectively, but no improvement was found in group 1. Significant improvements in EIA after the training periods were found in all training groups, but basal asthma improved most in group 3, probably due to the basal treatment with DSCG.