Abstract Calcitonin gene-related peptide is a 37-amino-acid neuropeptide which has a direct action on the heart and is an extremely potent vasodilator. Immunoreactive calcitonin gene-related peptide is present in plasma, cerebrospinal fluid and in other tissues. We have previously established the specific binding characteristics of this neuropeptide to the cerebellar membranes. This paper describes a sensitive, rapid and specific radioreceptor assay for the measurement of receptor-active calcitonin gene-related peptide in tissues and in plasma extracts using cerebellar membrane preparations as the binding agent. This assay should prove a valuable tool in studies of the physiology of this vasoactive neuropeptide and of its involvement in disease.