Osmotic minipumps were implanted in 4-wk-old female broiler chickens to supply a 2-wk continuous infusion of recombinant human insulin-like growth factor-I (rhIGF-I) in three doses (.03, .1, and.3 mg/kg BW per day). At the end of the experimental period no differences m BW were detected, although abdominal fat was significantly reduced in the highest dose group. Measurement of fat content in both breast and thigh muscle indicated a different effect of IGF-I treatment on these parameters, as no reduction was observed. Determination of circulating IGF-I levels revealed a twofold increase m the .3-mg group whereas the lowest dose chd not increase circulating plasma levels. The changes in IGF-I levels did not influence growth hormone levels whereas thyroxine levels were significantly decreased both m the .03- and .3-mg groups after 1 wk of treatment. At the same time Plasma triiodothyronine levels were increased in the .1- and .3-mg/kg groups. There results indicate that a continuous infusion of IGF-I did not increase weight gain but may play a role as a fat repartitioning agent.