A 99 to 100% pure preparation of rat kidney glomeruli was obtained by a simple procedure involving perfusion of rat kidneys with magnetic iron oxide suspended in Earle's balanced salt solution buffered with 1 (2 hydroxyethyl) piperazine 4 (2 ethanesulfonic acid). The glomeruli were isolated with the use of a permanent magnet which allowed tubules and other tissue contaminants which did not contain iron to be removed by decantation. The procedure described was superior to procedures based solely on sieving with regard to the purety of the preparation obtained and its adaptability to different sizes of animals. The iron containig glomeruli were as active as glomeruli isolated without iron in converting 14C labled oleic acid to 14CO2, indicating that he presence of the iron had no deleterious effect on metabolic activity. This would thus appear to be a simple system to study the effect of pharmacologic agents on isolated glomeruli without interference by tubules.