Assessment of canalization and crystallization of human cervical mucus and their variability during the menstrual cycle has revealed a direct relationship with ovarian hormone levels. This hormone dependence of cervical mucus was clearly identified during the fertile phase, while it seemed to be hormone independent during the infertile phases. In fact, during the early preovulatory and the postovulatory phase, both canalization and crystallization showed the same morphological features in spite of the striking difference in hormonal levels. On the basis of these data and the already known heterogeneity of cervical secretion, it is suggested that one of the mucus components is hormone dependent while the other is hormone independent, their quantity modifications being quite opposite during the menstrual cycle. The hypothesis therefore indicates two different types of muciparous cells in the cervical crypts: normal muciparous cells--as in the other mucous epithelia--intermixed with others only secreting under the stimulus of ovarian hormones.