A study of the efficacy of various methods for diagnosing normalcy of individual menstrual cycles under field study conditions was conducted. The study group consisted of ten women, 25 to 34 years old, who had intact reproductive tracts and regular menstrual cyclicity. They were working fulltime in jobs outside the medical field, had less than 1 year of college education, were not attempting to conceive, and were not using any birth control devices. The subjects were monitored for two complete menstrual cycles during which basal body temperature (BBT), salivary (SER) and vaginal mucous electrical resistance (VER) were measured daily, and urine samples were collected daily. The subjects were asked to manually evaluate their cervical mucous daily starting on day eight of each cycle. Blood samples were collected and transvaginal ultrasonography was performed every 6 to 9 days during the cycles. The saliva samples collected for VER measurement were analyzed for estradiol and progesterone. The blood samples were analyzed for serum luteinizing hormone (LH), estradiol, and progesterone. The urine samples were analyzed for LH, estrone-3-glucuronide (E13G), and pregnanediol-3-glucuronide (Pd3G). All hormone concentrations were determined using a radioimmunoassay (RIA). Urinary LH was also determined by the subjects themselves using a semiquantitative dipstick technique. Nineteen menstrual cycles were completed. One subject inadvertently did not complete one luteal cycle. Thirteen menstrual cycles were judged to be normal based on the urine LH, E13G, and Pd3G measurements. The remaining six cycles were considered to be abnormal. Seven of 13 LH surges detected by the RIA were not detected by the dipstick. The best correlations between the hormone concentrations were obtained with the urine samples. Changes in SER and VER were not predictive of changes in the cycles. BBT measurements misclassified 53% of the cycles. Evaluation of cervical mucous could not accurately predict the periovulatory periods. The transvaginal ultrasonic examination was able to visualize changes in ovarian structures that occurred during the cycles. The authors conclude that determining urine LH, E13G, and pd3G concentrations is the most informative and practical technique for studying menstrual function under field conditions. Transvaginal ultrasonography provides reliable information but is unsuitable for use in the field.