at high phosphate concentrations there is; less (approximately 50%) free endogenous tryptophan available to the culture because o f decreased activity oftryptophan synthetase, as compared to iow-phosphate culture. Further, when tryptophan was initially supplemented (100 mg/l) to the high-phosphate cultures, they also yielded 100 mg alkaloid per liter. The above results clearly indicate that high concentrations of inorganic phosphorous decrease the synthesis of tryptophan, ultimately inhibiting the synthesis of alkaloids. These observations further support our earlier findings [7J that tryptophan, due to its precursoric nature stimulates alkaloXd synthesis in Aspergittusfumigatus as it does in the clavicep,; species.