 the estrous cycle of rats can be quickly identified by observing the vaginal smears under a microscope. The smears can be examined at low magnification, 10x, to determine the presence of three cell types, squamous cells, columnar cells, and cuboidal cells. At higher magnifications, 40x, the columnar cells can be further distinguished into two subtypes, tall columnar cells and short columnar cells. These observations allow researchers to identify the estrous cycle stage of the animal. This article was authored by F. K. Markons, F. J. B. I. N. C. H. I. N. A. P. Tano.