Methods and apparatus are described where with living Kupffer cells can be procured from the liver of the rabbit and the dog for study and cultivation in vitro. Almost none of these cells can be dislodged from the normal liver by forcible perfusion; but after they have taken up finely particulate matter (India ink, iron oxide), they come away in great numbers. When they have phagocyted ferromagnetic iron oxide they can be selected with a magnet from amongst the blood elements present in suspension with them; and they are obtainable in quantity by this means. They do poorly when plated in a thin plasma clot, failing to multiply or to assume their characteristic shape; but they flourish when allowed to attach themselves to strands of lens paper bathed in serum that is frequently changed. Bacterial infection of serum cultures of Kupffer cells from normal rabbits and dogs occurs only as the result of secondary contamination of the materials, whereas it regularly develops in cultures from animals with fever induced by the injection of nucleic acid or of killed B. prodigiosus. Kupffer cells obtained under such conditions are abnormally active, and some can be washed out of the liver of sick animals in the absence of any preliminary phagocytosis of particulate matter. The facts have a bearing both on the conditions conducing to blood invasion and on the response of the Kupffer cells in the emergency. The characters of the isolated Kupffer cells and the results of tests of their presumptive functions will be described in later papers.