Abstract: Four Hu sheep fitted with chronic catheters at mesenteric vein and right hindquarter artery and vein were used to study the effect of clenbuterol on the amino acid net balance by means of determining the amino acid flow through their right hindquarter muscle.The results are as follows.In the control period,the total amino acid flows of the right hindquarter vein and artery were 4.54 mg/min and 5.48 mg/min,respectively.Compared with the control period,after injecting clenbuterol into the mesenteric vein,amino acid flow in right hindquarter vein and artery increased greatly (P<0.01):7.70 mg/min in the vein,9.61 mg/min in the artery,respectively.Of the 15 amino acids determined,in the experiment group,besides an obvious increase of the flow of all amino acids,a distinct increase could be found in the total quantity for 10 amino acids absorbed (Asp,Glu,Thr,Gly,Ala,Pro,Met,Val,Leu and Lys)and 3 amino acids released (Arg,His and Ser)by the hindquarter muscle (P<0.05).This indicated that clenbuterol could regulate amino acid net balance by altering the absorption or release of amino acids.