Embedding in large plastic blocks. Diagnostic light and potential electron microscopy on the same block.

Specimens destined for light and electron microscopy were fixed in a modified buffered formalin, postosmicated, dehydrated, and embedded in a mixture of epoxy resins (Epon-araldite) in large plastic molds. These blocks were sectioned at 0.5 to 1 micron on a JB-4 microtome and stained with a combined nuclear and cytoplasmic stain (Paragon). The sections were examined by light microscopy for diagnostic evaluation. If ultrastructural examination was also desired, the selected area was isolated using the "mesa" technique. The trimmed block was then sectioned on an ultramicrotome, picked up on grids, stained, and examined in the electron microscope. We think these techniques offer the diagnostic pathologist the potential of viewing 1-micron sections at a light microscopy level with the option of subsequent electron microscopy of the same area of the same block.