To test the existence of inherited liability to migraine, formal segregation analysis of family data collected from 128 patients has been performed. Patients were subdivided into three groups in accordance with the presence or absence of migraine in their parents. The results obtained in each group were then compared with those expected on the basis of two different modes of simple Mendelian inheritance, namely autosomal dominant and autosomal recessive transmission. Our data show that neither of the two hypotheses can be accepted. thus suggesting the existence of a possible genetic heterogeneity of liability to migraine.