A large number of natural and synthetic species ranging from virus particles to small polymer beads have been employed over trie years as labels in electron microscopic applications. Perhaps the most useful and versatile of these labels are the colloidal heavy metals. The colloidal labels can be synthesized as round regular spheres in sizes from 1 to 150 nanometers in diameter and thus can be used where molecular and sub-molecular ranges of spatial resolution are required. They are electron “dense” and good emitters of secondary and back-scattered electrons and hence are readily detectable in both scanning electron microscopic imaging systems and transmission electron imaging systems. Larger particles, 10nm and above, can be identified via their shape in force based imaging systems.