A new study, published in Cephalalgia, has revealed that PACAP-38-like immunoreactivity (PACAP-38-LI) is linked to phases of migraine. PACAP-38 is involved in activation of cerebral blood vessels. Tuka et al. assessed PACAP-38-LI in plasma during both ictal and interictal phases in 87 patients with migraine. Compared with healthy controls, patients had significantly lower PACAP-38-LI in the interictal phase. Migraineurs had elevated levels of PACAP peptide during the ictal phase relative to the interictal phase. Furthermore, a negative correlation between levels of interictal PACAP-38-LI and disease duration was identified.