Changes in beta-adrenergic receptors in the neurohypophysis and intermediate lobe of the rat have been characterized under physiological and stress conditions. Classical immobilization stress (IMO) was also combined with the immersion of rats into water (IMO + COLD stress). Both types of stress were applied for 30, 60 or 150 min. The intensity of stress stimuli were controlled by measuring the level of plasma ACTH. Changes in the level of plasma ACTH indicate that both types of experimental protocol induced reliable and reproducible stress conditions. Binding studies dealing with beta-adrenergic receptors in the intermediate lobe and neurohypophysis were performed in saturation binding studies by using of 125l-iodopindolol. Binding parameters, maximal binding capacity (Bmax) and dissociation constant (Kd) were assessed by nonlinear analysis with computer program Viewfit. In the neurohypophysis, no changes of Kd were found in the stressed animals. However, maximal binding capacity was decreased significantly with the increased exposure to the stress. In the intermediate lobe Kd values were slightly decreased and Bmax values decreased gradually with increasing duration of stress exposure. Our findings suggest that the process of receptor desensitization of beta-adrenergic receptors can also be detected under stress conditions in the neurohypophysis and intermediate lobe of the pituitary gland where it could contribute to the mechanisms involved in stress reactions.