This investigation deals with the potential additional value of serum CGRP measurements as compared to calcitonin in screening for medullary carcinoma of the thyroid (MTC) in families with multiple endocrine neoplasia type 2 (MEN 2). Basal as well as pentagastrin-stimulated values for CGRP are evaluated in relation to the corresponding levels for calcitonin. Serum CGRP is within normal range in most family members with pathological calcitonin response to the pentagastrin stimulation test. Furthermore, these potentially affected family members do not respond to the pentagastrin stimulation test with an increase in CGRP. Pentagastrin stimulation tests performed in patients with manifest MTC affect the serum CGRP levels inconstantly and in two patients, with elevated basal level of CGRP, stimulation caused a release of calcitonin while concentrations of CGRP remained unaffected. We conclude that determination of serum CGRP adds no information to that of serum calcitonin in MEN 2 family screening for MTC.