We will continue our investigation of the following unique aspects of the alkylating activity of L-phenylalanine mustard (alkeran, melphalan, sarcolysine): 1) the persistence of alkylating activity in plasma and the extended course of DNA alkylation in tumor cells, 2) the exceptionally high levels of in vivo attack on DNA observed by us and 3) the unusual preponderance of RNA alkylations over protein alkylations. In due course we hope to relate these molecular phenomena to the specificity of anti-tumor action.