 The short length of the rat's estrus cycle makes them ideal for investigation, and a fast and practical method was developed to determine the phases by collecting vaginal secretion every morning and observing unstained native material using a microscope without a condenser lens. Using the 10x objective lens, it is easier to analyze the proportion of cellular types, while the 40x objective lens helps recognize each type. The process takes only 15 to 20 minutes to determine the estrus cycle phase of all 30 female rats. This article was authored by F. K. Marcons, F. J. B. N. C. H. I. N. A. P. Tano