Oxidative metabolism in whole cells of Escherichia coli strain 82/r was inhibited by d-camphor when glucose, pyruvate, or succinate was used as substrate. Inhibition was not due to lower surface tension in d-camphor-treated cell suspensions nor was it a function of cell permeability. Succinic, lactic, and NADH-oxidase activities were inhibited in alumina powder cell-free extracts (80 μg of protein/ml) by d-camphor (1100 μg/ml). NADH: and succinic: DCPIP oxidoreductase enzymes were unaffected by d-camphor. Menadione (vitamin K₃) restored succinic, lactic, and NADH-oxidase activities in d-camphor-inhibited cell-free extracts. Concentrations of menadione used to restore succinic and NADH oxidase activities were not stimulatory in non-camphor-treated extracts. Succinic oxidase activity in d-camphor-inhibited cell-free extracts was also restored by ubiquinone (Q₆) but not by vitamin K₁. These results are interpreted to indicate that d-camphor may affect quinone function in E. coli.