Physical working capacity of the adrenalectomized Wistar rats can be augmented to some extent by training. This is not accompanied by increased unspecific resistance or augmented content of liver glycogen. The trained adrenalectomized rats revealed heart hypertrophy and increased activity of Mg2+-activated actomyosine ATPase in myocardium. After the training the physical worcing capacity was lower in adrenalectomized rats than in thyroidectomized ones. The 5-day administration of hydrocortisone failed to increase swimming time in adrenalectomized rats provided a high dose of progesterone was injected simultaneously. This can be due to the competition between progesterone and glucocorticoids for the glucocorticoid cytoplasmic receptor sites. The data obtained suggest that the effect of glucocorticoids on the physical working capacity is associated with their action on the adaptive protein synthesis.