Hepatocytes isolated from rats bearing line A of Walker 256 carcinoma (WA) were used to study the turnover of total liver protein and the synthesis of albumin in comparison with ad libitum (AL) and pair-fed (PF) healthy controls. The rates of total protein synthesis by hepatocytes of WA animals were 40 and 90% higher than in AL and PF controls, respectively. The degradation of fast-turnover proteins was not affected by nutrition or by the tumor, whereas the degradation of slow-turnover proteins was slightly but significantly increased--about 24% higher in hepatocytes from WA rats than in PF controls. The combination of the two processes, synthesis and degradation, was in favor of an increased synthesis which explains the increase in liver protein content observed in vivo in WA rats. Dietary restriction did not affect the synthesis and secretion of albumin, whereas the tumor significantly reduced its synthesis by about 30%. The plasma concentration of albumin in WA rats dropped by about the same percentage compared with AL and PF animals.