 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, swamous cells, columbar cells, and cuboidal cells. At higher magnifications, 40x, the columbar cells can be further distinguished into two subtypes, tall columbar cells and short columbar cells. These observations allow researchers to identify the estrous cycle stage of the animal. This article was authored by F. K. Marquans, F. J. B. A. N. C. H. I. and A. P. Tano.