The S, S-bis (" chloroet, hyl) carbarno) l derivatives of the ethyl esters of L-methionine, L- leucine, L-phenylalanine, L-glutamic acid, and L-aspartic acid were prepared by the reaction of bis (2-chloroethy1) aniine with the appropriate amino acid ethyl ester isocyanate. These cwmpounds were found to rearrange on addition of water to the corresponding urethans. These substances have undergone preliminary animal test, ing for ant'itunior activity.