This study was conducted to determine the effects of the oral administration of the beta agonist clenbuterol on body composition in growing rats reared under a high ambient temperature. Forty-three male Wistar-strain rats of 5 weeks of age were divided into 6 groups: 2 levels of ambient temperature (26 and 33 degrees C) and 3 dose levels of clenbuterol (0, 50, and 100 micrograms/kg diet) under each ambient temperature. All rats were raised for 7 weeks. From the 3rd week, rats in the clenbuterol-treated groups were fed a diet containing clenbuterol. Both the lipid and cholesterol content in the rat liver, and the epididymal adipose tissue weight were significantly higher in the hot environment than in the temperature environment. Body fat component was significantly higher in rats in the 33 degrees C groups in comparison with that in rats in the 26 degrees C groups. On the other hand, body protein component was significantly lower in the 33 degrees C groups than in the 26 degrees C groups. Although the administration of clenbuterol significantly decreased fat and increased protein in the 26 degrees C groups, no particular influence of clenbuterol administration on body composition was observed in the 33 degrees C groups.