A short-term estrogen test was used to obtain a correct cytologic diagnosis in 73 patients with an equivocal atrophic cellular pattern. Overestimation in cytodiagnosis was markedly eliminated, and the correct cytologic diagnosis was made in 81% of the cell samples after the estrogen test. The purpose of this study was not only to confirm the usefulness of the short-term estrogen test, but also to observe the cytomorphologic changes before and after the test. Thick cytoplasm, vacuoles in the cytoplasm, and a distinct cell border increased, while the amorphous chromatin pattern was eliminated after the estrogen test. Maturation of atypical cells in cases of dysplasia, carcinoma in situ, and invasive squamous-cell carcinoma was investigated before and after the estrogen test. Although malignant cells were not influenced by estrogen, maturation of dysplastic cells was induced after the test.