This study demonstrates the presence of calcitonin gene-related peptide (CGRP) in human cerebrospinal fluid (CSF) using specific and sensitive radioimmunoassay, together with gel-permeation and high performance liquid chromatography (HPLC). The median immunoreactive CGRP (i-CGRP) level from 158 CSF specimens was 8.0pmol/l, as measured with an antiserum recognizing the whole molecule of CGRP (CC-2/1) and 12.0 pmol/1 with an antiserum recognizing the C-terminal region of CGRP (CG-39). CSF samples with high protein concentration (>0.6g/l) had a median level of i-CGRP of 18.4pmol/l when measured with antiserum CC-2/1 and 23.0pmol/l with CG-39, while samples with ‘normal’ protein concentrations (<0.6 g/1) had much lower values, with median levels of 7.0 and 11.0 pmol/l, with the two antisera, respectively. Gel-permeation chromatography and HPLC studies revealed multiple peaks of i-CGRP, consistent with forms with different molecular weights. However, on HPLC, the major peak of i-CGRP corresponded to the elution position of the synthetic hCGRP(1–37) and was able to bind to a CGRP specific receptor preparation suggesting that it may be biologically active.