Oil red 0 and Sudan black B are commonly employed to examine the lipid content of frozen sections from muscle biopsy specimens.1 These techniques often yield suboptimal results that are difficult to interpret because of extraneous dye precipitate. In order to circumvent these problems, we have devised an osmium tetroxide-p-phenylenediamine procedure similar to that used for the staining of epoxy-embedded sections.2
We cover the frozen sections with a few drops of cacodylate-buffered 2% osmium tetroxide solution for 30 s to one minute. Generally, we use osmium tetroxide solution that is "left over" from the osmication of tissue for electron microscopy. The sections are washed briefly with distilled water and then covered for 10 to 15 s with a 2% solution of p-phenylenediamine in 70% alcohol. The sections are again washed briefly and placed under a coverslip with water. For permanent preparations, the stained sections