1. Phosphorus utilization by S. griseus has been studied during its fermentation. Both organic and inorganic phosphorus are steadily taken up during aerobic process, while during anaerobiosis the levels of phosphorus recorded a gradual increase after an initial fall. 2. From the chromatograms of different phosphate esters present in the mycelial extracts of S. griseus, it appears that the Embden-Meyerhof cycle is operative during anaerobiosis, while some other pathway, possibly the hexose monophosphate shunt, proceeds during aerobic growth. © 1956, All rights reserved.