THERE has been isolated from yeast1, crude oryzanine2and impure cozymase3an unusual nucleoside which on acid hydrolysis yields adenine and a thiomethyl-sugar. Falconer and Gulland4claim to have demonstrated that the thiomethyl-sugar and adenine are combined at the 9-position of the base. The thiomethyl-sugar has been the subject of several investigations; thus Suzuki et al.2,5and Levene and Sobotka6have shown that the thiomethyl group is retained during osazone formation, thereby excluding positions 1 and 2 of the sugar as the sites where it is combined. The thiomethyl-sugar could be readily reduced to a thiomethylpentitol, which on oxidation with lead tetra-acetate yielded 0.9 mol. of formaldehyde7, indicating that position 3 in the sugar cannot be the combining position of the thiomethyl group. Satoh and Makino8adduced further evidence which excluded also the C4of the pentose as the site of the thiomethyl substituent. Previously, Wendt7, using titration data obtained by the Willstätter–Schüdel method, had shown that the thiomethyl-sugar obtained by acidic hydrolysis of the nucleoside was an aldose. Hence all the available evidence indicated that the derivative was a 5-thiomethylpentose.