Invertase and Yarrowia lipolytica cells were coimmobilized in polyelectrolyte complex (PEG) microcapsules prepared from sodium cellulose sulfate and poly(dimethyldiallylammonium chloride). With these studies on coimmobilization of enzymes and viable cells, the question of supplying the substrate from a nonmetabolizable substance was addressed. It was shown to be favorable to immobilize the enzyme prior to encapsulation onto an insoluble carrier material in order to avoid leakage of the enzyme from the capsules. Small particles of poly(aminomethyl styrene) were used to immobilize the enzyme successfully by covalent binding via glutaraldehyde. After preimmobilization and encapsulation of polystyrene-bound invertase, 17% of the initial activity was retained. The growth and product formation profiles of the microorganisms were changed by coimmobilization of the invertase-polystyrene complex, and the capsule stability and cell-retaining ability of the PEC capsules were significantly increased as a result of supplying the carbon source in the capsule interior. The coimmobilized cell/enzyme-carrier complex was subjected to 800-1000 h of continuous fermentation. The productivity, however, was considerably lower than that of Y. lipolytica cells encapsulated alone, without invertase. The mean production rate of citric acid by the coimmobilized enzyme/cell system was 0.014 g citric acid l(-1) h(-1) in comparison to 0.125 and 0.25 g l(-1) h(-1) by the encapsulated and free cells, respectively.