Analysis of the culture filtrates of lysergic acid alkaloid-producing fermentations at intervals during growth of the cultures showed that phosphate is most rapidly depleted from the medium in fermentations that produce the highest levels of alkaloid. In view of the known interference with phosphate metabolism by arsenate, sodium arsenate was added to the culture medium with the intent of creating, in effect, a phosphate deficiency. The addition of arsenate at levels between one-fiftieth and one-twentieth the molar concentration of phosphate resulted in increases in alkaloid production up to 100 per cent. Experiments with ten-times the usual concentration of phosphate showed that the ratio of arsenate to phosphate rather than the absolute concentration of arsenate was most significant in obtaining this effect. Increasing the concentration of phosphate alone (up to twenty times the usual concentration) resulted in substantial increases in alkaloid production. The effect of arsenate on both the rate and the extent of phosphate uptake was determined. Among several inhibitors of electron transport and/or oxidative phosphorylation, only the un coupler of oxidative phosphorylation (dinitrophenol) was effective in increasing alkaloid production.