Although the triptans have greatly improved the acute treatment of migraine headache, there are yet many shortcomings. Therefore, new strategies for the treatment of migraine are needed which offer advantages over current therapy, e.g. triptans. Our novel approach was based on the hypothesis that the release of calcitonin gene-related peptide (CGRP) could play a causative role in migraine headache. Thus we initiated a program aimed at the design and synthesis of small molecule CGRP receptor antagonists. High throughput screening led to the identification of (R)-Tyr-(S)-Lys dipeptide-like compounds that showed weak but unequivocal binding to the human CGRP receptor. Lead optimization afforded highly potent CGRP antagonists, the prototype being compound 19 (BIBN4096). This compound exhibiting a favorable biological profile was selected for initial clinical trials. A proof of concept study indicated that intravenous application of 19 was effective in the treatment of acute migraine headache. This finding strongly supports our initial working hypothesis that CGRP plays an important role in the pathophysiology of migraine.