The effect of glucose and cyclic 3',5'-adenosine monophosphate (cAMP) on the synthesis of glucoamylase and alpha-amylase by the yeast Endomycopsis fibuligera str. 20-9 was investigated. The glucoamylase synthesis was inhibited by every concentration (0.05--3.0%) of glucose. The synthesis of alpha-amylase was significantly reduced by high concentrations (2.0-3.0%) of carbohydrate only. An addition of cAMP (1 X 10(-5) M) reversed compeltely the inhibitory effect of 0.5-2.0% glucose on the alpha-amylase synthesis and partially restored the glucoamylase synthesis. It is concluded that catabolite repression may be involved in the regulation of alpha-amylase and glucoamylase synthesis by Endomycopsis fibuligera str. 20-9 and that this type of regulation shows varying effectiveness in the enzyme synthesis.