Cervical mucus arborization in the Rhesus monkey.

Cyclic variations in the quality of cervical mucus were evaluated in the monkey. A characteristic pattern was observed. On the day before ovulation maximal fern production was noted, with a dramatic regression in fern pattern in the subsequent day. A consistent correlation with changes in vaginal cytology was not observed. Daily examination of fern pattern provides a reliable index for ovulation timing in the monkey.