Cervical mucus forms channels when dried under a coverslip. The aim of the present work was: 1) to prove mucus canalization both in spontaneous ovulatory cycles and during ovulation induction with gonadotropins; 2) to prove the estrogen dependence of this phenomenon; 3) to check the importance of the proteidic and electrolytic concentration on chaneling; and 4) to use this phenomenon clinically, shortening the time in which it occurs. The number and arrangement of channels vary during the cycle. The phenomenon is estrogen-dependent. The comparison between estradiol values and the number of channels during spontaneous ovulatory cycles and treatment with gonadotropins showed a linear relationship. Treatment with estradiol 17 beta-valerate and ethinyl estradiol induced channel formation in women with primary amenorrhea. Canalization and ferning disappeared after dialysis or treatment with proteolytic enzymes. It follows that the two phenomena have similar characteristics. Canalization increases daily, as does estradiol, whereas ferning maintains the same grade for a longer period, and when a grade of + + + is reached, it provides no further indications. With the use of a thermostat, canalization occurred in only a few hours. Chaneling, a more precise index, could therefore substitute for ferning, particularly when monitoring the induction of ovulation.