The distribution and transcapillary exchange of albumin have been studied in patients with congestive heart failure and the results compared with a group of control subjects who did not have heart failure.The normal relation between vascular albumin mass and plasma volume on the one hand and transcapillary albumin exchange on the other does not exist in patients with congestive failure. The transcapillary albumin exchange rate, which presumably reflects capillary permeability, is decreased relative to the plasma volume and vascular albumin mass. It appears that decreased permeability of capillaries to albumin is associated with congestive failure and may be responsible for the increased plasma volume characteristic of this disease.The appearance of labeled protein in edema fluid has been studied in 7 patients and compared with the simultaneously determined serum disappearance curves. The albumin contained in the edema fluid constitutes a small fraction of the total extravascular albumin pool. The vascular albumin mass equilibrates less rapidly with the local edema albumin mass than with the total extravasenlar albumin mass.