Arginine was transferred from arginyl-tRNA to the amino-terminal end of chromatin proteins by L-arginyl-transferase. The reaction was dependent on the presence of potassium ion and beta-mercaptoethanol and was sensitive to RNase and trypsin. Treatment with DNase partially inhibited the transfer of arginine from arginyl-tRNA suggesting that intact chromatin structure is necessary for modification of chromatin. The radioactivity incorporated into chromatin was sensitive to trypsin but not to DNase or RNase. Most of the incorporated radioactivity was recovered in the phenol fraction, supporting the notion that modification of chromatin takes place in proteins but not in nucleic acids of chromatin. Modification of the proteins by transfer of arginine from arginyl-tRNA takes place mainly in the nonhistone fraction of chromatin. Major portions of chromosomal proteins modified in this manner appear to be released from chromatin. Incubation of incorporated radioactive product with [12C]arginyl-tRNA did not alter the product, showing that incorporated arginine is stable and does not exchange with added arginine or arginyl-tRNA. These observations suggest that aminoacyl-transferase may function in the modification of chromosomal proteins and that modification of chromatin may alter the regulatory mechanisms of cellular functions.