Hypoalbuminemia, a frequent finding in cancer patients, can be demonstrated in the tumor-bearing rat. In actuality, the circulating amount of albumin is maintained in tumor-bearing rats, although total body water and plasma volume are increased. The fractional degradation rate of newly synthesized albumin labelled by the injection of carbon-14-carbonate was significantly increased in tumor-bearing rats (half-life 55 hours) as compared with control rats (half-life 85 hours). These findings indicate maintained synthesis of albumin in the tumor-bearing rats, a finding consistent with an increased ratio of specific activity in albumin to that in plasma urea after the injection of carbon-14-carbonate. Hypoalbuminemia in cancer seems to be the net result of an increased turnover rate of albumin and dilution of the maintained albumin mass. Despite the presence of cancer anorexia, the flux of substrates from the degradation of peripheral tissues is sufficient to supply the liver and, in turn, to enable an increased protein synthesis with maintenance of the synthetic rate of albumin.