When adenine was added to the non-growing cell medium of Eremothecium ashbyii, riboflavin production of the mold was increasingly inhibited with increasing concentration of adenine. Under these conditions, a cationic compound was accumulated in the mycelia. The compound was isolated from the mycelia and highly purified. The purified compound was proved to be S-adenosylhomocysteine through IR analysis. In the control experiment, or in the addition of other purines which stimulated riboflavin production of the mold, another cationic compound was accumulated in the non-growing cells. The compound was largely accumulated in the presence of both adenine and methionine, isolated from the mycelia and purified. The purified compound was concluded to be S-adenosylmethionine through IR and NMR analyses. The significance of these compounds on the riboflavin biosynthetic pathway was argued under "Discussion".