A series of quatemary N-methylated analogs of D-Arg-2dermorphin tetrapeptide was synthesized by solid phase method. Two N-methylation analogs, H-Tyr-D-Arg-Phe-Y(+Me3)-NH2 [Y = Lys (1) and Om H-Tyr-D- Arg-Phe-, (2)], and a compound, H-Tyr-D-Arg-Phe-Dab-NH2 (7), which was obtained as a by-product in this study, showed high in vitro biological properties. These compounds also showed potent in vivo antinociceptive effects (8. c.) in the mouse writhing test and the in vivo effect was antagonized markedly by Nmethyllevallorphan, suggesting that they can produce a high degree of peripheral antinociception in mice.