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A method for the simultaneous measurement of gastrointestinal protein loss and total albumin turnover entailing the use of a combination of (125)iodine- and (51)chromium-labeled albumin is described. Albumin turnover was calculated by the measurement of albumin-(125)I plasma decay and cumulative urinary excretion, and the results obtained agreed closely with previous studies utilizing albumin-(131)I. Gastrointestinal catabolism was calculated from the rate of fecal excretion of (51)Cr and the specific activity of plasma albumin-(51)Cr, and these data were related to the calculated albumin turnover results. During the period of 6-14 days after administration, the ratio of specific activties of albumin-(125)I and -(51)Cr in plasma and in extravascular spaces or gastric and biliary secretions remained almost identical. Fecal excretion of (51)Cr was also quite stable at this time. In six normal subjects gastrointestinal catabolism accounted for less than 10% of total albumin catabolism. Excessive gastrointestinal protein losses did not contribute to the low serum albumin in three patients with cirrhosis or in two adults with the nephrotic syndrome. Multiple mechanisms leading to hypoalbuminemia were demonstrated in other subjects with a variety of gastrointestinal disorders.