Young adult obese Zucker rats have altered tissue fatty acid (FA) composition. The present study was aimed at determining whether such changes were seen in either liver, serum or adipose tissue obtained from 17-day-old obese (fafa) rats in comparison to both homozygous (FaFa) and heterozygous (Fafa) lean rats. Body weights of obese pups (30.3 g) were significantly greater than those of homozygous lean rats (25.2 g) (P<0.05). Liver weight and lipid content were similar in all groups. Inguinal fat pad weight and lipid content were greatest in obese pups (573 mg) followed by heterozygous lean pups (303 mg); homozygous lean pups (146 mg) had the lowest values. There were no differences among the groups in hepatic FA composition in either triacylglycerol (TG) or phospholipid fractions. Serum TG was similar among the groups, while serum phospholipid was greater (P< 0.05) in obese (269 mg/dL) than in homozygous lean pups (184 mg/dL); heterozygous lean pups had an intermediate value not significantly different from either homozygous group. On a percent basis, there were no differences in FA composition in either serum lipid fraction among the three groups. There were a number of significant differences in adipose tissue FA composition between the groups on a percent basis. The adipose tissue FA composition on a percent basis reflected that of maternal milk. The results indicate that suckling obese Zucker rats do not have tissue FA profiles that are characteristic of essential FA deficiency.