SUMMARYSome chemical changes which took place in the mycelium of Aspergillus Jlavus during autolysis were studied. A . Jlavus underwent a ' neutral autolysis' in which a decrease of 73.9% in mycelial dry weight occurred. Glucose, xylose, maltose and mannitol were found in autolysing mycelium of A.Jlavus. The loss of free glucose amounted to 10 mg./flask during the whole period of autolysis. Xylose was decreased to half its initial content by the third day of autolysis and then disappeared by the ninth day, whereas maltose decreased at the beginning and then remained constant from the eighty-first to the hundred and eleventh day of incubation. Eighty-nine per cent of the initial amount of mannitol was lost during the first 9 days of autolysis, whereas fat seemed to be uninvolved in the process. Eighteen different amino acids were found in the autolysing mycelium of A . Jlavus. The general picture was of decreasing concentrations during autolysis, and amino acids decreased their content by about 95% with respect t o the concentration present at the beginning. This decrease partially accounted for the loss of mycelial-nitrogen observed during autolysis.