Silver methenamine impregnation: a useful adjunct to renal electron microscopy.

The application of silver methenamine impregnation (SMI) to renal electronmicroscopy (EM) has been relatively neglected, but the technique has proved to be a useful aid in renal biopsy diagnosis. Tissues for SMI were fixed in glutaraldehyde/osmium and were embedded in either L.R. White resin or Epon. En-bloc staining of tissue with uranyl acetate was undertaken, but this procedure is considered optional. In our hands the technique has been valuable in the rapid assessment of renal ultrastructure in "routine" biopsies and especially in the diagnosis of complex or subtle changes in a variety of subtypes of glomerulonephritis, including the early membranous, familial-Alport type, mesangiocapillary and difficult to classify categories.