The aim of the present study was to investigate the acute effect of CABG (coronary artery bypass graft) surgery on the rates of synthesis of muscle protein, the positive acute-phase protein fibrinogen and the negative acute-phase protein albumin. Synthesis rates of muscle protein, fibrinogen and albumin were measured simultaneously before and 4 h after the end of surgery from the incorporation of L-[(2)H(5)]phenylalanine (given at 43 mg/kg of body weight) in 12 patients undergoing CABG surgery. Surgery was performed either with the use of extracorporeal circulation with cardiopulmonary bypass (on-pump; n=5) or with the beating heart procedure without cardiopulmonary bypass (off-pump; n=7). Post-surgical muscle protein fractional synthesis rates were decreased by 36+/-6.5% compared with pre-surgical values (1.59+/-0.10 compared with 0.97+/-0.08%/day respectively; P<0.001). In contrast, the synthesis rates of both fibrinogen (36+/-4 compared with 100+/-11 mg.day(-1).kg(-1) of body weight; P<0.0001) and albumin (123+/-12 compared with 178+/-19 mg.day(-1).kg(-1) of body weight; P<0.001) were both significantly increased after surgery. No significant differences were found between surgery performed with or without cardiopulmonary bypass. In conclusion, the results demonstrate that CABG surgery has a profound effect on protein metabolism, with a differential response of protein synthesis in muscle and liver.