The concentration of calcitonin gene-related peptide (CGRP) in rat tissue extracts was determined by a specific and sensitive radio-immunoassay, and the distribution of its specific binding sites was assessed by radioligand binding studies. A high concentration of immunoreactive CGRP was found at all levels of the spinal cord, in the trigeminal nucleus, in trigeminal and dorsal root ganglia, in the thyroid gland, in blood vessels and in nerves. The highest density of specific binding sites was detected in the cerebellum, where the CGRP content was minimal. The dorsal portion of the spinal cord contained a high concentration of CGRP and its specific binding sites. Specific binding of 125I-CGRP was also demonstrated in a number of other areas of the brain and in certain peripheral tissues. Among the other tissues examined, the spleen, adrenal gland, penis, lungs, bladder, heart and blood vessels all contained a large number of CGRP binding sites, whereas only a negligible number of sites were found in ganglia, nerves, muscle, kidney and liver. The distribution of CGRP and its specific binding sites demonstrated here suggests that CGRP is a neuropeptide with multiple physiological roles.