The chromosomal ispA gene encoding farnesyl diphosphate synthase of Escherichia coli was disrupted by inserting a neo gene cassette. The null ispA mutants were viable. The growth yield of the mutants was 70% to 80% of that of the wild-type strain under aerobic conditions, and was almost the same as the wild-type under anaerobic conditions. The levels of ubiquinone-8 and menaquinone-8 were both significantly lower (less than 13% and 18% of normal, respectively) in the mutants than in the wild-type. The undecaprenyl phosphate level in the mutants was modestly lower (40% to 70% of normal) than in the wild-type strain. Thus the synthesis of all-E-octaprenyl diphosphate, the precursor of ubiquinone-8 and menaquinone-8, was decreased more severely than that of Z,E-mixed undecaprenyl diphosphate, the precursor of undecaprenyl monophosphates, under the conditions where the synthesis of farnesyl diphosphate was decreased. The condensation of isopentenyl diphosphate with dimethylallyl diphosphate was detected in the cell-free extracts of the mutants, although it was 5% of that in the wild-type strain. A low level of farnesyl diphosphate seems to be synthesized in the mutants by other prenyltransferases such as octaprenyl diphosphate synthase or undecaprenyl diphosphate synthase.