The time-course of the oleandomycin content in the mycelium and fermentation broth-filtrate was studied by the microbiological assay at different periods of cultivation of strains 471 and 961 in fermenters and flasks containing a rich soybean-corn medium. It was shown that centrifugation of the mycelium over the sucrose density gradient induced a 25-80 per cent decrease in its moist weight at the expense of removal of the admixture components of the rich medium. Addition of glucose (2 per cent) to the culture-grown in a lactose medium by the 72nd hour of fermentation had no effect on further increase of the cell biomass. However, it lowered the content of the mycelium-fixed and excreted antibiotic at all the subsequent fermentation periods. The content of oleandomycin in the untreated mycelium was only 0.36 per cent of its content in the fermentation broth filtrate. After centrifugation of the mycelium over the sucrose density gradient and its intensive washing with distilled water the content of the mycelium-fixed antibiotic decreased still more. The time-course of the content of the mycelium-fixed and excreted oleandomycin was characterized by the presence of two activity peaks; by the 80-110th and by the 140-170th hour of cultivation.