The presence of both alpha- and beta-calcitonin gene-related peptide (CGRP) was demonstrated by oxidation and by CNBr cleavage in extracts of plasma, cerebrospinal fluid and spinal cord in man. This was achieved by the use of both CNBr cleavage and oxidation of the methionine residue present in the human beta-CGRP molecule. This study demonstrates that around 50% of CGRP immunoreactivity in plasma, cerebrospinal fluid and spinal cord is not alpha-CGRP, but corresponds to beta-CGRP-like activity. Furthermore, experiments with CNBr also suggest the presence of another methionine-containing CGRP-like peptide in all three extracts.