The synthesis of the following dipeptides is described: L-arginyl-L-asparagine acetate, L-arginyl-L-glutamine acetate, L-arginyl-L-lysine diacetate, and L-arginyl-L-ornithine diacetate. The two former were prepared by coupling a mixed anhydride of α-carbobenzoxy-ω-nitro- L-arginine directly with L-asparagine or with L-glutamiae; catalytic hydrogenolysis of the resulting intermediates gave the dipeptides. The two others were obtained by combining α-carbobenzoxy-L-arginine with ω-carbobenzoxy- L-lysine methyl ester hydrochloride or with ω-carbobenzoxy-L-ornithine methyl ester hydrochloride in the presence of N,N′-dicyclohexyl-carbodiimide; saponification and hydrogenation was necessary to uncover the resulting dipeptides.