AbstractThe ability ofUstilago maydis(DC.) Cda. to grow and to produce lysine and threonine was investigated in shake flask cultures. Growth and production of lysine and threonine increased markedly when aeration was increased. The optimal ratio of glucose to diammonium phosphate in the medium seemed to be approximately 10:1. Ammonium phosphate, ammonium sulfate, ammonium chloride, ammonium nitrate, sodium nitrate, urea, aspartic acid, glutamic acid, and glycine were readily used as nitrogen sources. Growth and amino acid production was poor on ammonium carbonate, ammonium acetate, ammonium citrate, trimethylamine, and betaine.U. maydis(DC.) Cda. was found to grow on a number of different carbohydrates. Besides D‐glucose the organism could utilize D‐mannose, D‐galactose, D‐fructose, L‐arabinose, D‐xylose, D‐ribose, sucrose, maltose, and the polyalcoholes D‐sorbitol, D‐mannitol, andi‐inositol. Pectin, dextrin, and corn starch treated with α‐amylase could also be used but not untreated corn starch or lactose, cellobiose, D‐sedoheptulose, glycerol, or D‐glucosamine. The formation of lysine and threonine was better with disaccharides and hexoses than with pentoses.No specific effects on the formation of lysine and threonine could be observed from changes in the concentration of calcium, sodium, potassium, magnesium, zinc, iron, copper, manganese, cobalt, or molybdenum. The requirement of metal io