Carbon-13 NMR spectroscopy was used to study the effects of the peroxisome proliferator perfluoro-n-decanoic acid (PFDA) on hepatic carbohydrate metabolism in male Fischer-344 rats. The data indicate that PFDA-treated rats display an inhibition in hepatic [1-13C]glucose and [3-13C]alanine utilization on day 5 posttreatment. PFDA rats show hepatic mean glucose and alanine intensities which are significantly greater (ca. 10-100%) than controls. With [1-13C]-glucose as substrate, PFDA rats show severe to complete inhibition in glycogenesis on days 3 and 5 posttreatment. With [3-13C]alanine as substrate, both groups show functional gluconeogenesis and glycogenesis; however, treated rats show a more transient and less intense C1-glycogen resonance relative to control. These data suggest that PFDA inhibits either the hepatocellular transport of glucose and/or its phosphorylation by glucokinase. The effect of PFDA on TCA cycle activity was determined by monitoring the flow of [3-13C]alanine into glutamate. The relative activity of pyruvate carboxylase (PC) versus pyruvate dehydrogenase (PDH) is represented by the ratio of the glutamate NMR signal intensities (C2 + C3)/C4. PFDA rats show a lower (C2 + C3)/C4 glutamate ratio, suggesting greater relative activity of PDH versus PC in PFDA rats relative to controls. Differences in PDH activity may arise from differences in lipolytic activity. Our data suggest a dysfunction in fatty acid metabolism in PFDA rats and corroborate other studies which show that PFDA inhibits fatty acid oxidation.