The effect of dichloroacetate on rates of gluconeogenesis was studied in isolated parenchymal cells obtained from the livers of normal fasted rats. Dichloroacetate significantly inhibited glucose formation from endogenous substrates and from added precursors (e.g., lactate, pyruvate, or glycerate) which enter the gluconeogenic pathway prior to the level of glyceraldehyde-3-phosphate dehydrogenase (GPDH). In contrast, dichloroacetate did not significantly affect glucose synthesis from precursors (e.g., fructose, or glycerol) which enter beyond the GPDH-catalyzed step. Lactate production from fructose of glycerol was unaffected by dichloroacetate. Inhibition of gluconeogenesis occurred regardless of the apparent effects of dichloroacetate on the redox state of the cytosol. Dichloroacetate produced variable effects on the lactate-pyruvate substate pair, while it consistently produced a more oxidized state in the beta-hydroxybutyrate--acetoacetate couple. Unlike uncoupling agents, dichloroacetate reduced glucose synthesis without stimulating respiration or altering total adenine nucleotide levels or ATP/ADP ratios. Dichloroacetate did not affect the metabolism of lactate or pyruvate to CO2 or glycogen. It did, however, significantly inhibit conversion by the cells of added lactate to pyruvate and glucose or of added pyruvate to lactate and glucose.