The involvement of the pineal gland in the regulation of the initial ACTH reactive outflow to short-term stress inducement was studied. The stress trial, consisting of the subcutaneous saline injection in the animal hind leg, elicited ACTH release, the peak appearing in the 5th min followed by a rapid downturn to the prestress level in the 15th min. The higher ACTH level in the pinealectomized rats was monitored in the 5th min. The results obtained show the implication of the pineal gland in restricting the magnitude of the initial stress-reactive ACTH outflow.