Protein metabolism after surgery in the presence of disseminated malignancy has been investigated and compared with results obtained from patients undergoing similar surgical procedures for benign disease and localized malignancy. Whole body nitrogen turnover, measured by primed continuous infusion of 15N glycine, was highest with disseminated malignancy. Similarly rates of whole body protein synthesis and breakdown, calculated from turnover and nitrogen excretion (nitrogen intake being zero), were elevated in the presence of disseminated malignant disease. The increased rates of protein metabolism may represent adaptation to the demands of inevitably growing malignant tissue.