In order to investigate the cytological pictures of lochia and influences by sex hormones, the cytological examination by Papanicolaou's staining was daily performed on lochia of 80 normal and abnormal puerperas during the 7 days after delivery. The discharge was taken from the posterior fornix of vagina by usual small sponge. Ishikawa's classification was employed for that of vaginal epithelial cells. The percentage of the keratinized cells (keratinization-index) was obtained by microscopic examination performed to avoid the thickend parts as far as possible. The result derived from the observations is as follows, 1) Although the cytological pictures of lochia markedly differ with the individual patients, there is present the definite picture with the process of puerperum. 2) The change of keratinization-index is one of the most reliable basis for diagnosing the transition of the cytological pictures, in which the 10 th gestational month shows the lowest value, beginning to rise at the onset of labor and then the highest is obtained on the first day of postpartum, after which time the rapid lowering is found. 3) The keratinization-index does not demonstrate the absolute quantity of estrogens, but the estrogenic activities as a whole in perplexing endocrine system. As has been stated, the cytological pictures of lochia demonstrate the definite changes after labor and, furthermore, have the close relationship to the sexual functions. This procedure is, therefore, of great importance for recognizing the healing process of puerperal involutions of genital organs and the transitions of the sexual functions.