Radioautography and conventional counter methods have been used to determine the relative amount and localization of I131albumin in a number of tissues at 3, 30, and 60 min. after intravenous injection. Certain tissues showed essentially no change in albumin content with time, others contained extravascular albumin which increased with time, and the liver and adrenal evidenced a decreasing level of albumin with time. The transcapillary passage of albumin and its accumulation in extravascular compartments are correlated with tissue structure.