Crystal patterns of cervical mucus were observed by electron scanning microscopy in 6 normal women and in women taking oral contraceptives, on Days 5, 11, 14 and 21 of the menstrual cycle. The pills contained 500 mcg norgestrel and 30 mcg ethinyl estradiol (Indian Drugs and Pharmaceuticals Ltd., Hyderabad). Mucus was obtained by aspiration from the cervical canal, smeared and dried at room temperature, and plated for scanning microscopy without fixation. Spinnbarkheit and ferning was noted to increase on Days 11 and 14 in normal cycling women, but rose slightly between Day 5 and 11 and then remained constant in pill cycles. On the scanning microscope, mucus from cycling women was characterized by fern patterns on Days 11 and 14. On Day 11 a rounded, parallel, grooved backbone with flattened branches on only 1 side was observed. The distance between sub-branches was consistent at 3.33 mcm. On Day 14 sub-branching lessened, but branching was commonly located on both sides of the backbone. The distance between sub-branches ranged from 3.75-5.0 mcm. The width of the main backbone was wider than on Day 11, from 6.25-11.25 mcm. In women on the pill, no ferning appeared: mucus remained thick, viscous and tenacious, with no crystalline structure.