Historically, CGRP receptors have been classified as CGRP 1 or CGRP 2 subtypes, chiefly depending on their affinity for the antagonist CGRP 8 - 3 7 . It has been shown that the complex between calcitonin receptor-like receptor (CRLR or CL) and receptor activity modifying protein (RAMP) 1 provides a molecular correlate for the CGRP 1 receptor; however, this does not explain the range of affinities seen for CGRP 8 - 3 7 in isolated tissues. It is suggested that these may largely be explained by a combination of methodological factors and CGRP-responsive receptors generated by CL and RAMP2 or RAMP3 and complexes of RAMPs with the calcitonin receptor.