Marshall , K. C. (Cornell University, Ithaca, N. Y.) and M. Alexander . Nitrification by Aspergillus flavus . J. Bacteriol. 83: 572–578. 1962.— Aspergillus flavus has been shown to produce bound hydroxylamine, nitrite, and nitrate when grown in peptone, amino acid, or buffered ammonium media. Free hydroxylamine was not detected in these cultures, but it was found in an unbuffered ammonium medium in which neither nitrite nor nitrate was formed. Evidence was obtained for the presence of β-nitropropionic acid in the filtrate of an actively nitrifying culture. Alumina treatment of an ammonium medium prevented the formation by growing cultures of nitrite and nitrate but not bound hydroxylamine. The effect of alumina treatment was reversed by the addition of 10 −3 m CeCl 3 to the medium. Extracts of the fungus contained peroxidase and an enzyme capable of catalyzing the production of nitrite from β-nitropropionic acid. The nitrite-forming enzyme is apparently specific for β-nitropropionate; no activity was found with nitromethane, nitroethane, and nitropropane as substrates. Nitrate was not reduced to nitrite nor was nitrite oxidized to nitrate by the hyphal extracts. The significance of these observations in nitrification by A. flavus is discussed.