Alternative splicing of RNA transcripts from the calcitonin gene produces mRNAs that encode different polypeptides. While the mRNA encoding calcitonin predominates in thyroidal 'C' cells, calcitonin gene-related peptide (CGRP) mRNA appears to be the major mRNA component in non-thyroid tissue, including brain. The predicted peptide arising from translation of CGRP mRNA has now been identified immunocytochemically throughout the central and peripheral nervous systems. CGRP, a 37-residue peptide, is distributed in brain pathways subserving sensory, motor and autonomic functions. We report here that CGRP acts in the central nervous system to stimulate selectively noradrenergic sympathetic outflow.