We have recently devised a nucleotide triplet code which meets one of the requirements for being the correct solution to the “coding problem” in biology (Woese, 1961). This code was designed to, and does, predict the nucleotide composition of each of the six ribonucleic acid viruses, tobacco mosaic, tomato bushy stunt, southern bean mosaic, turnip yellow, cucumber, and polio, from their particular amino acid compositions. Because the protein and nucleic acid compositions of the six viruses vary considerably, it is probable that the code, while not unique, is one of a relatively small number of closely related codes, all of which fit the experimental data (Yčas, 1960). In the present communication we shall develop this code further.