The effect of glucose on alpha toxin production was studied in the Wood 46 strain of Staphylococcus aureus. Optimal toxin production occurred when 0.2% glucose was present in the medium. Omission of glucose gave lower yields of toxin, and concentrations of 0.5% and higher severely depressed toxin formation. Glucose affected the initiation of alpha toxin synthesis in growing cultures. As the glucose concentration increased, the time lag prior to the onset of toxin production also increased, and maximal rates of synthesis were not obtained until essentially all the glucose had been exhausted from the medium. The addition of glucose to toxin-producing cultures caused a temporary, almost complete repression of toxin formation which was not due to pH changes in the culture. The synthesis of most extracellular proteins was not inhibited during the period of repression. After recovery, toxin was produced at rates equal to those of untreated control cultures. The kinetics of toxin repression and the observation that the glucose analogues, 2-deoxy-d-glucose and alpha-methyl-glucoside, as well as other carbon sources, inhibit toxin production suggest that transient repression is responsible for the inhibition of toxin formation. No evidence for a regulatory role of adenosine 3', 5'-cyclc monophosphate in alpha toxin production was obtained.