The effect of a simple, low intestinal obstruction has been investigated in dogs on the leakage of 131I-serum albumin from the circulation into the intestine. An increase leakage has been demonstrated. In the distended segment of the intestine above that ligation a significant increase in protein-bound radioactivity, from the normal value of 0.082 plus or minus 0.012 ml/10 cm intestine/hour to 0.276 plus or minus 0.068 ml/10 cm intestine/hour, was obseved which means a more than 3fold increase. The values for albumin leakage did not change in the more proximal segments of the intestine less involved in the distension namely in the duodenum and the jejunum, furthermore in the ileal segment below the ligation. The increase in albumin liadage observed during intestinal obstruction resulted in 33% rise of total catabolism.