Sephadex globules placed as landmarks in combined stereo microscopy, scanning and transmission electron microscopy.

Regions of specific interest in tissue blocks were localized in a stereo microscope and landmarked with Sephadex spheres (10-40 micron in diameter). This procedure made it possible to recognize these regions easily and quickly in the scanning electron microscope. When the tissue was later embedded in Epon the spheres facilitated orientation when sectioning. Thus it was possible with great certainty to determine the level at which ultrathin sections should be cut for transmission electron microscopy to attain an exact correspondence between scanning and transmission electron microscopic observations. The procedure is described and an example of its application is shown in a study of experimental hypertensive endothelial changes.