A pituitary protein, designated 7B2, was demonstrated to be present in the cerebrospinal fluid (CSF) obtained from control subjects and patients with various cerebrovascular accidents (CVAs). Although there was not any significant difference in mean immunoreactive 7B2 concentrations among various CVA groups, the CSF immunoreactive 7B2 levels in control subjects were 10 to 100 times higher than those in control plasma samples. Immunoreactive calcitonin gene-related peptide (CGRP) and immunoreactive atrial natriuretic peptide (ANP) levels in the CSF were comparable to those in corresponding normal plasma samples. The CSF ANP concentrations in patients with cerebral bleeding and subarachnoid hemorrhage were significantly lower than those in control subjects. Gel chromatography or high-performance liquid chromatography indicated that the main immunoreactivities of 7B2, CGRP, and ANP coeluted with corresponding standard material. The high CSF concentrations of immunoreactive 7B2 observed might indicate a functional role of 7B2 in the central nervous system.