Reductones such as ascorbic acid and 5-methyl-3,4-dihydroxytetrone (enediol), scorbamic acid (enaminol) and mercapto-hydroxycoumarine (thiolenol) degraded polysomes as well as ribosomal RNA in ribosome particles in vitro. They caused significant changes in amino acid incorporation by polysome and pH 5 enzyme system or liver slices with endogenous RNA or poly U as the messenger. The results suggested the possibility that reductones affect protein synthesis through the breakage of mRNA and rRNA and give some clues elucidating processes between DNA breakage and cytodifferentiation or cytoanomalization demonstrated as Yamafuji's effect.