In 1928 Papanicolaou1 demonstrated his ability to make a diagnosis of cancer of the uterus by the observation of single malignant cells cast off from the tumor into the vaginal secretion. This was a cytologic diagnosis rather than a diagnosis made by a study of the architecture of the tissue, such as is done by pathologists. Subsequently, in 1941 and 1943, Papanicolaou and Traut2 published articles and a monograph describing their experiences. The monograph, illustrated by many plates of benign and malignant cells, suggested to the medical profession that their method was a success and should be used. In 1943 Meigs and others,3 confirming the work of Papanicolaou, reported a series of cases studied at the Massachusetts General Hospital and in 1945, in a second article,4 gave convincing evidence of the value of the method. At present 2,749 cases with an error of only 3.2 per