We have found a correlation between the certain characteristics of primary structure and biologic activity in exorphins and endogenous opioid peptide family. The characteristics of primary structure are the content of certain segment pairs as well as the density of their arrangement in a peptide. These segment pairs represent basic elements of the regulatory peptide primary structure pattern, which was found recently [Dokl. Akad. Nauk USSR 289 (1986) 721–724; Int. J. Peptide Prot. Res. 38 (1991) 505–510].
