When malabsorption develops during the course of Whipple's intestinal lipodystrophy, it is often accompanied by hypoalbuminemia. Among 53 case reports published between 1951 and 1964 for which values of the concentration of albumin in the serum were presented, there were 43 values below 3.5 g per 100 ml (Figure 1).A decrease in the concentration of albumin in the serum may be due to dilution or to a decrease in the size of the body's total exchangeable pool of albumin. A reduction in the albumin pool size may result from decreased synthesis, from increased catabolism or loss, or from both causes. To explore the factors responsible for the hypoalbuminemia of Whipple's disease, we studied the albumin metabolism of seven patients with this disorder. Albumin labeled with 131I or with 125I was used to measure the total exchangeable pool of albumin and the rates of albumin catabolism and synthesis. Albumin-51Cr was used to measure loss of albumin into the gastrointestinal tract. The patients were studied when their disease was in relapse and again when therapy had induced marked improvement. The data suggest that abnormal exudation of serum protein into the gastrointestinal tract is an important factor in causing the hypoalbuminemia of Whipple's disease, that treatment of the disease can reverse this exudative enteropathy relatively rapidly, and that impairment of al-