The role of the pituitary-adrenocortical system (PACS) in body adaptation abilities was studied on rats. The adaptation abilities were tested by a body working capacity (the running time in a treadmill till fatigue). The single administration of ginseng results in the increase of a working capacity up to 132%, the seven-day one up to 179%. This makes it possible to speak about two levels of adaptation, each being characterized by a specific PACS status and a degree of PACS involvement in adaptation abilities. The single administration of ginseng is accompanied by an increase in the basal level of ACTH and corticosteroids. At a 7-day administration the basal level of ACTH and corticosteroids does not change but PACS reactivity to the immobilising stress increases. The preliminary administration of 15 mg/100 g b. w. hydrocortisone, 7 days before testing of the working capacity and PACS status, causes the block in PACS function. It results in the decrease of the basal corticosteroid content in plasma and the inability of stress factor to cause the rise in the corticosteroid level. The PACS blocking results in the decrease of a working capacity in normal rats not treated with ginseng and in animals singly treated with ginseng. The PACS blocking effected the increment in a working capacity caused by a 7-day ginseng administration to a lesser extent, however, the decrease in a working capacity took place even in this case. The conclusion is made that PACS status changes with the transition of a body to a higher level of adaptation: PACS excitation occurs or the system excitability increases.(ABSTRACT TRUNCATED AT 250 WORDS)