Properly performed and interpreted serial vaginal smears constitute the simplest, cheapest, most practical, and most reliable method of estrogen assay in the human. The results of such smears may be used as a guide to adjusting dosages in the treatment of patients with estrogen deficiencies. Estrogens, synthetic or natural, should be used in adequate amounts without fear of carcinogenesis for the prevention of osteoporosis, the control of atherogenesis, and the achievement of a sense of well-being. If the vaginal smear shows evidence of estrogen deficiency, patients undergoing natural or induced menopause should be treated with estrogenic preparations in the presence or absence of symptoms. Vaginal cytograms should be used as widely in our daily practice as the differential count of white blood cells in the initial diagnosis and in the follow-up program.