Summary.1. In Ehrlich ascites tumour cells partially blocked with malonate, the accumulation of citrate and alpha ketoglutarate was raised during aerobic glycolysis upon the addition of fumarate and citrate respectively.2. Fumarate, in contrast to citrate or alpha ketoglutarate, counteracted the Crabtree effect in cells partially blocked with malonate, in both the presence and absence of DNP. After a lag time succinate counteracted the Crabtree effect in trans‐aconitate blocked cells. The data suggest that during aerobic glycolysis respiration is limited by substrate phosphorylation(s) in the alpha ketoglutarate — succinate react