The predominant application of virion electrophoresis, whether in solution or agarose or acrylamide gels, has been for purposes of characterizing a virus, or simply discriminating between closely related, and even serologically indistinguishable, isolates. Agarose gel electrophoresis has also been used to monitor conformational states of intact spherical virions. Although agarose gel electrophoresis of intact virions has been used for a long time, a review of the literature indicates considerable refinement in the technique and it appears to have become the method of choice. Polyacrylamide/agarose gels have been used to purify turnip yellow mosaic virus, tobacco mosaic virus (TMV), and to analyze TMV disassembly intermediates. Isoelectric focusing has proven to be a very powerful technique useful in resolving, characterizing and evaluating the purity of proteins. An interesting application of virion typing by electrophoresis was described by Hurtt et al.