Formalin fixation for electron microscopy: a re-evaluation.

Several common formaldehyde fixative solutions using various buffer systems were evaluated for use with both light and electron microscopy. Ultrastructural detail was judged best using formaldehyde buffered with monobasic sodium phosphate and sodium hydroxide, which is easy to prepare and of such low cost that it serves as an excellent routine fixative for all specimens. A parallel series of specimens, half of which were fixed in this solution and half in Millonig’s phosphate buffered paraformaldehyde, demonstrated no obvious variations in ultrastructural preservation due to the 10 to 15% methanol present in formalin. The need for preselection of tissue to be subsequently examined ultrastructurally is unnecessary if this fixative is used routinely in the histopathology laboratory.