The aim of this study was to investigate the interaction between long-chain fatty acids (LCFA) and growth hormone (GH) in the regulation of liver fatty acid binding protein (LFABP) and peroxisome proliferator-activated receptor-α (PPARα). Cultured rat hepatocytes were given oleic acid (OA; 500 μM) and GH (100 ng/ml) for 3 days. LFABP mRNA increased 3.6-fold by GH and 5.7-fold by OA, and combined incubation with GH and OA increased LFABP mRNA 17.6-fold. PPARα mRNA was decreased 50% by GH, but OA had no effect. Hypophysectomized (Hx) female rats were treated withl-thyroxine, cortisol, GH, and dietary fat for 7 days. PPARα mRNA levels were three- to fourfold higher in Hx than in normal female rats. GH decreased PPARα mRNA 50% in Hx rats. Dietary triglycerides (10% corn oil) increased LFABP mRNA and cytosolic LFABP about twofold but had no effect on PPARα mRNA in Hx rats. GH and dietary triglycerides had an additive effect on LFABP expression. Dietary triglycerides increased mitochondrial hydroxymethylglutaryl-CoA synthase mRNA only in the presence of GH. The diet increased serum triglycerides in Hx rats, and GH treatment prevented this increase. Addition of cholesterol to the diet did not influence LFABP levels but mitigated increased hepatic triglyceride content. In summary, these studies show that GH regulates LFABP expression independently of PPARα. Moreover, GH has different effects on PPARα-responsive genes and does not counteract the effect of LCFA on the expression of these gene products.