The difference in the growth on fructose between differentiated and adifferentiated variants of Streptomyces roseoflavus var. roseofungini should be attributed to their different capacity in forming the enzyme system for fructose uptake whose action is induced by this carbohydrate. In the cells of the two variants grown on glucose and mannitol, the process of induction occurs in the presence of chloramphenicol. In the cells grown on glycerol, chloramphenicol inhibits the induction. The growth of the differentiated variant on fructose stops apparently due to the exhaustion of endogenous reserves which are necessary for maintaining the system of fructose uptake in the active state.