The levels of plasma epinephrine (E) and norepinephrine (NE) were examined in rats exposed to hypokinesia in special adjustable cages for 1, 7 and 75 days. One day before the collection of blood an arterial catheter was inserted into the tail artery and blood samples were collected from undisturbed animals on next day at 8 a.m. and after 1, 6, 12 and 24 hours later. The control groups of animals were kept single in standard animals cages. The content of E, NE and corticosterone was determined in plasma. In rats exposed to hypokinesia for the first time a marked increase of plasma E and NE levels were observed at 1 hour in forced restriction and both E and NE remained elevated after 6, 12 and 24 hours of hypokinesia. A permanent increase of NE and E content in plasma was found in rats exposed to hypokinesia for 7 and 75 days. However, the plasma corticosterone levels were increased only during the first day of hypokinesia, at 7 and 75 days no significant changes in plasma corticosterone were noted. These results showed that there is an important increase of plasma catecholamine levels immediately after the beginning of hypokinesia and the activation of sympathoadrenal system is maintained during the whole period of hypokinesia. No significant changes in adrenocortical system activity were noted during the long-term hypokinesia.