A fluorescent antibody method of staining the juxta glomerular cells (JG-cells) of wax-embedded renal tissue, initially prepared by freeze-substitution, was developed. Specimens of antisera to pig renin, specially absorbed by low-renin pig kidney powder stained only the granules of the JG-cells of the pig kidney. These antisera also cross-reacted with the JG-granules of dog and rabbit. When plasma globulins were elevated in the dog, globulin deposits could be stained with conjugated antibodies to canine globulins inside the JG-cells. Because of this finding the JG-cells were judged to be highly permeable to plasma constituents and perhaps angiotensinogen.