1. Glomeruli free from renal tubules and cell debris were isolated in large numbers from rat kidney cortex by a rapid, simple process of graded sieving on stainless steel meshes. 2. Glomeruli were viable, had fragments of the arterioles attached and contained renin. 3. Glomeruli, when incubated, released renin into the medium. Using a super-fusion technique this was shown to be time dependent until a basal secretion level was achieved. 4. Release of renin was directly proportional to the number of glomeruli and could be stimulated by isoprenaline, adrenaline and noradrenaline in order of the potency of their action on beta-adrenoreceptors. 5. Isolated glomeruli were therefore established as a useful model system for studying the release of renin by direct influences on the juxtaglomerular cells where haemodynamic, tubular and extrarenal influences are removed.