Candida utilis CBS 621 was grown in chemostat cultures at D = 0.1 h-1 on glucose, xylose, gluconate, acetate, or ethanol as the growth-limiting substrate with ammonia or nitrate as the nitrogen source and analysed for NADPH-producing and NADPH-consuming enzyme activities. Nitrate and nitrite reductases were strictly NADPH-dependent. For all carbon sources, growth with nitrate resulted in elevated levels of HMP pathway enzymes. NADP+-linked isocitrate dehydrogenase did not vary significantly with the NADPH requirement for biosynthesis. Growth on ethanol strongly enhanced activity of NADP+-linked aldehyde dehydrogenase. Neither NADP+-linked malic enzyme nor transhydrogenase activities were detectable under any of the growth conditions. The absence of transhydrogenase was confirmed by the enzyme profiles of cells grown on mixtures of glucose and formate. It is concluded that the HMP pathway and possibly NADP+-linked isocitrate dehydrogenase are the major sources of NADPH in Candida utilis.