GH is reported to acutely decrease hepatic D3 activity in the chicken (Darras et al., 1992a) to cause increased circulating T3 levels. The diminished hepatic D3 activity observed in leptin-treated chickens could be a secondary response to augmented GH action on the liver. In line with our presumption, hepatic expression of GHR and IGF-I was found significantly up-regulated in leptin-treated chickens. GH secretion is known to be decreased in ob/ob mice (Larson et al.,1976), suggesting leptin's involvement in the regulation of GH secretion. Studies in rats have shown that leptin stimulates both basal and GH-releasing hormone (GHRH)-induced GH secretion (Carro et al., 2000). Because GH secretion is pulsatile in nature and a specific antibody against chicken GH is not available, GH was not measured in the present study, but the up-regulated hepatic GHR and IGF-I mRNA expression may indicate enhanced GH action in the liver.