In 40 rats immobilized for 30 hrs, a reduction of density of distribution of the adrenergic neural terminals in myocardium occurs along with changes of the cardio-vascular functions. The death of animals in immobilization was due to a progressive drop of arterial pressure. Immediately before death the density reduction of adrenergic terminals was the most obvious. Disturbances of the cardio-vascular functions in immobilization stress seem to be related to the reduction of density of the adrenergic neural terminals distribution in the myocardium.