As a consequence of alternative RNA processing events, a single rat gene can generate messenger RNA's (mRNA's) encoding either calcitonin or a neuropeptide referred to as alpha-type calcitonin gene-related peptide (α-CGRP). An mRNA product of a related gene has been identified in rat brain and thyroid encoding the protein precursor of a peptide differing from α-CGRP by only a single amino acid. The RNA encoding this peptide, which is referred to as β-CGRP, appears to be the only mature transcript of the β-CGRP gene. Hybridization histochemistry reveals a similar distribution of α- and β-CGRP mRNA's, but their relative levels of expression vary in different cranial nerve nuclei. Thus β-CGRP is a new member of a family of related genes with potential functions in regulating the transduction of sensory and motor information.