Scanning electron microscopy, a relatively young discipline, has been used mainly for research purposes and very seldom as a diagnostic procedure. A study was made of normal and abnormal kidneys by light, transmission and scanning electron microscopes. Normal human and rat kidneys were examined under the scanning electron microscope but cellular detail was not clearly defined. Tissue was then cryofractured, critical-point dried, sputter-coated and examined again. Scanning electron microscopy then revealed greater cellular detail. Rats were injected with a solution of 0,6% uranyl nitrate in normal saline, and cryofractured sections were examined. Pathological changes were seen in the glomerulus as well as in the tubules. Scanning electron microscopy, while not replacing conventional modes of examination, can provide a rapid third dimension in the diagnosis of renal lesions.