SUMMARY A 4-month period of physical training increased the physical working capacity of 16 asthmatic children (aged between 9 -3 and 13*6 years) by a mean of 11 %. The increase was greater in boys and was negatively correlated with pretraining capacity. Urinary excretion of adrenaline, measured during a submaximal exercise test, decreased during the training period; the decrease was correlated with the increase in working capacity. Before the training period, exercise induced an increase in the plasma cortisol level; no increase was evident after training. In contrast, the training did not affect the exercise-induced increase in the plasma growth hormone level.