A series of CD measurements were carried out on members of peptides in the endothelin and sarafotoxin families. The helical structures taken by these peptides containing the helical motif with the sequences of Cys-X-X-X-Cys and Cys-X-Cys [Y. Kobayashi et al. (1991) Neurochemistry International Vol. 18, pp. 525-534] are classified into three groups: a group of structures of ET-1, ET-2 and vasoactive intestinal contractor (VIC), a group of sarafotoxin, and a group of ET-3.