After feeding rats for 3 weeks with clofibrate specific activities of the liver mitochondrial enzymes glycerol-3-phosphate dehydrogenase (G3PDH) and NAD-linked isocitrate dehydrogenase (NAD-ICDH) were found to be increased in a large particle fraction 6-fold and 1.6-fold, respectively, whereas the activity of NADP-linked isocitrate dehydrogenase (NADP-ICDH) remained unchanged. Possibly these effects contribute to the hypolipidemic action of clofibrate.