Within three patient groups (1. advanced renal failure, 2. patients under chronic hemodialysis, 3. patients with renal transplants) 16 serum proteins were determined immunochemically employing MANCINIS method. The group mean values for each protein were compared, and the statistical significance of intergroup differences was examined. The most noteworthy results were the following: a distinct increase in prealbumin in all groups, least marked in the dialyzed patients; frequent elevation of alpha2-macroglobulin in the patients with transplanted kidney, but not in the other two groups; a significant increase in beta2-glycoprotein in all groups. Other changes affected several components of the acute phase reactants which were, in part, markedly elevated. On the other hand, alpha1-antitrypsin and transferrin remained largely within the normal range. Possible mechanisms accounting for some of these changes are discussed.