Technical Abstract: The uncoupling proteins are thought to be involved in waste heat production, reducing the energy efficiency of growth in animals. Previous studies have detected their presence in swine and their regulation by the endocrine system. This study attempted to determine whether the uncoupling proteins 2 and 3 contribute to the increased heat production observed in somatropin treated swine. The data demonstrate that the uncoupling proteins are responsive to somatotropin treatment in finishing swine. Secondly, uncoupling protein response is highly tissue specific. Correlation analysis indicated a potential role for insulin like growth factor 1 in the regulation of the uncoupling proteins. These results suggest the possibility to manipulate the efficiency of growth in finishing animals by altering the expression of genes associated with heat production and metabolism at a time when changes in body composition can be critical for improving profitability.