Tryptophan analogs known to act selectively on protein synthesis were used to study the effects of tryptophan depletion on the formation ofStaphylococcus aureus(Wood 46 strain) toxic material. The production of toxin during growth and its presence in culture supernatants were followed by determining alpha hemolytic activity in rabbit blood agar, lethality for mice, and immunodiffusion patterns with staphylococcal antitoxins. The following results were obtained when the bacteria were grown in the presence of 4- and 5-methyltryptophans and 7-azatryptophan: (1) growth inhibition from 20 to 50%; (2) loss of alpha hemolytic activity; (3) inability of culture supernatants to kill mice; (4) decrease in the number of antigens precipitating with staphylococcal antitoxin and absence of reaction with purified alpha antitoxin. No significant effects were observed with 5-fluorotryptophan; 6-methyltryptophan was totally inactive. All inhibitions were reversed byL-tryptophan, anthranilic acid, and indole, but only partially by chorismic acid, and not at all by shikimic acid. These observations are suggestive of a predominant role ofL-tryptophan in the synthesis of staphylococcal alpha toxin.