This report describes the characteristic features of the exfoliated cells according to histological types, such as the type of early cervical adenocarcinoma for the diagnosis of cervical carcinoma of adenoid type (hereinafter called cervical adenocarcinoma). Further, the characteristics of cervical adenocarcinoma and its histogenesis were studied in an ultrastructural approach and we obtained the following results. 1) The exfoliated cells of adenocarcinoma in situ (hereinafter called AIS) show the characteristic features that assist the early detection of cancer. 2) The histological types for diagnostic use in characterizing the exfoliated cells are clear cell adenocarcinoma and adenosquamous carcinoma. Further, the histological structure of both well differentiated and poorly differentiated endocervical types can be deduced from the cytologic features. 3) Since the transitional cells of both squamous and columnar types and also the intestinal epithelial metaplastic cells were ultrastructurally observed in adenosquamous carcinoma and adenoacanthoma, the reserve cells are considered to act as an original cell and eventually participate in the histogenesis of these types of carcinomas. 4) The cells of both secretory granules and tonofibrils were detected in the AIS foci. This finding indicates the involvement of the subcolumnar basal cells which can eventually be differentiated into the secretory or ciliated cells of the columnar epithelium of the endocervical canal during the histogenesis of cervical adenocarcinoma of the endocervical type.