SUMMARYMixed + and - cultures produced 3 to 5 times as much carotene as either isolate produced when grown alone. Increasing the glucose concentration from 20 to 80 g/l more than doubled the carotene yield from mixed + and - cultures; this increase in glucose concentration resulted in an insignificant increase in carotene production when the + and - isolates were grown separately. Hexoses (glucose, mannose, and galactose) were the best carbon sources for carotene production by mixed + and - cultures. Glutamic acid was the best nitrogen source. The lipid content of the mycelium increased as the glucose content of the medium increased; the lipid content was approximately 50 per cent when the medium contained 100 g/1 of glucose. Carotene synthesis continued for several days after the glucose was utilized; the lipid content decreased after the glucose was exhausted. The addition of potassium acetate to 3-day-old cultures grown on the basal medium increased carotene production somewhat. Experiments with acetate-1-C14showed that acetate was utilized.beta-Ionone stimulated carotenogenesis markedly when it was added to half-grown + and - cultures; it was relatively ineffective when added to separate cultures of either isolate. In addition,beta-ionone inhibited growth, decreased the rate of glucose utilization and lipid synthesis, reduced the rate of respiration, and delayed zygospore formation and maturation. Yields of carotene slightly in excess of 7 mg/g dry mycelium were obtained from 4-day-old cultures grown on a molasses-glutamic acid medium and which were treated with 5μl ofbeta-ionone per culture on the second day of incubation.