The ability to synthesize ascorbic acid was demonstrated. The monosaccharides mannose, glucose, fructose, galactose and xylose were shown to act as precursors. Mannose proved to be the best and xylose the poorest substrate. A disaccharide, sucrose, was also utilized in the synthesis of ascorbic acid. Glucoronolactone gave inconclusive results. The following conditions were most favorable for ascorbic acid synthesis: substrate cencentration of 5x10-3 , pH 6.8, 3 hr. incubation period, temperature range of 25°-30°C, and 20% homogenate concentration. Addition of Mn++ to the incubation mixture did not result in any increase in the synthesis. Homogenates of fat bodies synthesized greater amounts of ascorbic acid than whole homogenates.