Cell free extracts of Thielaviopsis paradoxa grown on L-alanine as the sole source of nitrogen contained L-alanine dehydrogenase that catalyzes the oxidative deamination of L-alanine to equimolar amounts of pyruvate and ammonia . Lalanine dehydrogenase formation takes place during the logarithmic phase of growth .Maximal growth and enzyme formation were obtained at the 4 th day of growth .The optimum pH for growth and enzyme synthesis was 4.0 . L-alanine dehydrogenase was induced by a great variety of nitrogen sources , but L -alanine , DL-alanine, Ltheronine and ammonium phosphate were the most potent inducers . L-alanine concentration of 2.1 g/ l was found to be optimum for both growth and enzyme synthesis . L-alanine dehydrogenase formation was increased with increasing concentrations of ammonium phosphate in the growth medium ; the optimum concentration was 2.6 g/ l . The effect of different carbon sources and metal salts on growth and enzyme production was studied .