Active Hexose Correlated Compound (AHCCTM), an extract from several basidiomycetes, has been known as a biological response modifier (BRM) in humans as well as in animals. In the present study, AHCC was tested for its ability to modulate the hormonal responses to immobilization stress in the rat. AHCC at 3% in drinking water was given to male Wistar rats for one week, then rats were exposed to immobilization for 1 h. At 1 h after immobilization, the serum levels of corticosterone, norepinephrine, epinephrine, dopamine and glucose were increased significantly. Except for the corticosterone levels, all of these changes were restored to control levels by the AHCC pretreatment. These results suggest that AHCC can protect various effects induced by immobilization by attenuating the sympathetic nerve activity.