Vasopressin (VP), given intracerebrally to rats, can induce antipyresis, motor disturbances, and increases in arterial blood pressure. The possibility that the VP-binding sites in the fundus striati (FStr) could participate in these effects was investigated. After a bilateral injection of 100 pmol of VP into the FStr, the fever induced by an injection of the lipopolysaccharide of Escherichia coli (50 micrograms/kg ip) was not affected. Bilateral injections of 100 pmol of VP did not induce motor disturbances or alterations in body temperature after either of two successive injections. In contrast, bilateral injections of VP into urethan-anesthetized rats induced dose-dependent increases in arterial pressure without affecting heart rate. This increase was blocked by a V1 antagonist; oxytocin and a V2 agonist were ineffective. In keeping with this preliminary pharmacological analysis, radio-ligand-binding studies of the FStr revealed binding sites in the FStr exhibiting a binding profile typical of the V1 subtype. This study suggests that the V1 receptors in the FStr could participate in the central regulation of the blood pressure.