The effects of concentration of glucose, carbon sources, nitrogen sources, acetate, beta-ionone, temperature, pH, and light on the production of carotene by Choanephora cucurbitarum were studied. The yield of carotene increased as the glucose concentration was increased to 80 g/l. Good yields of carotene were obtained from glucose, mannose, fructose, and galactose; intermediate yields were obtained from maltose and cellobiose; and poor yields from xylose, L-arabinose, lactose, sucrose, and cellulose. Glutamic acid was the best nitrogen source while ammonium sulf ate was the poorest. The addition of potassium acetate, 0.49 g/1, to a glucose-glutamic acid medium increased the yield of carotene. The addition of beta-ionone, 5 [mu]l/culture, to 3-day-old cultures growing on a glucose-glutamic acid medium resulted in a 5-fold increase in carotene production. The effect of beta-ionone depended upon the time of addition, the amount added, and the composition of the medium. Carotene production was reduced when the initial pH was lower than 5.6; 28[degree]C was better than 25 or 20[degree]C. More carotene was produced in darkness than in light. All of the above results were obtained with mixed + and -cultures.