Carnitine, biosynthesized from the essential amino acid lysine, has been considered as the shuttling of long-chain fatty acid acyl residues into the matrix of mitochrondria for β-oxidation. This lysine-carnitine relation was studied in pregnant rats nourished with diets differing in lysine and protein content. Pregnancy seems to be a factor contributing to the increase of the free carnitine fraction and phospholipids in the liver, whatever the diet allowed. In the case of nonpregnant rats, free carnitine levels decrease and triglycerides increase in the liver when they are nourished with a low-protein and lysine-deficient diet