Chromic Phosphate Cr-51 is a radiopharmaceutical compound that has been extensively used in nuclear medicine. When administered intraperitoneally, the particulate form of chromic phosphate is pocketed in various areas of the peritoneum, or filtered out by the first lymph nodes encountered, because of the too large particle size, whereas the colloidal form is carried over to the lymphatic system. The larger particles originally present in its size spectrum or formed in vivo by aggregation of smaller particles are trapped by the first line of lymph nodes, and the remainder goes into the thoracic duct, with posterior incorporation into the blood circulation and final removal by the reticuloendothelial system: liver, spleen and bone marrow.