Publisher Summary This chapter discusses the purification of natural human-immune interferon (Hu-IFN) induced by A-23187 and Mezerein. The greatest obstacle in purifying natural immune interferon has been due to its relative instability. This is, particularly relevant when the material has been subjected to a variety of manipulations (e.g., dialysis, concentration, and adjustments in pH). A procedure is described for the purification of natural Hu-IFN, which overcomes this obstacle. The method takes advantage of sequential chromatographic techniques and immune interferon's biochemical characteristics. The controlled pore glass (CPG) is purchased from Electro-Nucleonics. The pore size is 350 A and the mesh 120–200. Fresh beads are added to 300 ml of 66% nitric acid, stirred, and allowed to settle. The nitric acid is then decanted, and the beads are washed (by stirring and settling) repeatedly in approximately 2 liters of water until the pH of the water is approximately 5.0. The data in the chapter demonstrate the efficiency of the procedure. The overall purification of the final product is greater than 70,000-fold. The overall recovery is approximately 33%. The peak gel-filtration fraction (number 35) represents a greater than 300,000-fold purification and a recovery of 18%.