Human renin gene restriction fragment length polymorphisms (RFLP) were compared in a Japanese family which has a high incidence of essential hypertension. 2. RFLP of human renin gene were observed in three restriction enzymes, Mbo I, Bgl I and Hind III; 1.4 kb and 1.0 kb [Mbo I], 5.0 kb and 9.0 kb [Bgl I] and 9.0 and 6.2 kb [Hind III]. 3. Plasma renin activity was not associated with blood pressure. 4. Renin gene RFLP were not cosegregated with essential hypertension in this Japanese family.