Formation of N-acetylkanamycin amidohydrolase (NAKA) in a strain of Streptomyces kanamyceticus proceeded in parallel with the increase of both kanamycin (KM) and N-acetylkanamycin (NAK) in the initial period. NAKA formation then suddenly began to decrease in NAK but KM continued to increase before reaching a maximum level. The study on conversion of intracellular NAK into KM using washed cells has shown that the endogenous activity of NAKA is most efficiently induced by acetate together with the activity of isocitrate lyase and N-acetyltyrosine amidohydrolase. Sclerin (SCL) stimulated their induction in the same manner, while N-acetyltyrosine repressed NAKA. Glucose effect was relieved by SCL and some amino acids. From these results, change in the chemical composition of cells in idiophase was well elucidated.