Abstract Glucose and glycerol, singly or when added in combination spared the utilization of endogenous glycogen of both larval and adult Taenia taeniaeformis during aerobic and anaerobic incubations. Significant glycogen synthesis occurred only when larvae were provided aerobically with both glucose and glycerol. It is suggested that the factor determining whether glycogen synthesis takes place is the amount of substrate absorbed, since the greatest influx was found under aerobic conditions with both glucose and glycerol present in the medium. Anaerobically, the substrate utilization was almost as large as that occurring aerobically, but much more succinic acid was produced in the absence of oxygen, suggesting that substrate carbon available aerobically for glycogen synthesis was diverted anaerobically to catabolic reactions. The carbon balances indicated that glycerol may have been used also for synthetic processes leading to compounds other than glycogen. The utilization of glucose, glycerol, or a mixture of both compounds led qualitatively to identical endproducts: Succinic, lactic, and acetic acids. The amount of succinic acid produced depended not only on the availability of oxygen, but also on the amount of substrate consumed. The carbon balances indicate that the formation of succinic acid may involve carbon dioxide fixation. The production of lactic and acetic acids, on the contrary, surprisingly was independent of the amount of substrate absorbed and the availability of oxygen. The average molar ratio of lactate to acetate was 1:1. It is possible that both acids originate from dismutation of pyruvic acid and that this reaction proceeds at a maximal rate at relatively low levels of substrate utilization.