A gamma-emitting colloid used in scintillation scanning of the reticuloendothelial system (RES). After intravenous administration, technetium Tc 99m sulfur colloid is phagocytized by the reticuloendothelial system and concentrated in the liver, spleen, and bone marrow; detection/localization of phagocytized gamma ray-emitting colloid is performed with a gamma-ray scintillation camera. Scintillation scanning using technetium Tc 99m colloid sulfur helps determine the distribution and function of the RES and the extent to which tumor involves the RES. The RES includes cells types that can phagocytize and sequester inert particles and vital dyes; RES cell types include macrophages or macrophage precursors, specialized endothelial cells lining the sinusoids of the liver, spleen, and bone marrow, and reticular cells of lymphatic tissue and of bone marrow. orA substance being studied as a way to find cancer in the body. It is also used to find sentinel lymph nodes in breast cancer. It contains a radioactive substance called technetium linked to a substance called sulfur colloid. Sulfer colloid is taken up by special cells in lymph tissue, and in the liver, spleen, and bone marrow after it is injected. A machine or probe that detects radioactivity is used to find where the technetium Tc 99m sulfur colloid is in the body. It is a type of radiopharmaceutical and a type of radioimaging agent. Also called Tc 99m sulfur colloid and Tc-99m SC.