Predicting ovulation is useful for managing the infertile patient and when done sufficiently in advance for fertility regulation by periodic abstinence. It has been reported that ovulation could be predicted by measurement of salivary and vaginal electrical resistance (SR and VR). These data from 32 menstrual cycles of 23 women were obtained to evaluate this technique. Data of 14 cycles were from subjects receiving clomiphene citrate (CC), while the others were from spontaneously ovulating subjects. A peak in SR was seen 5-7 days before the day of the LH peak in both natural and CC cycles. A correlation coefficient (r) of 0.94 was seen for the day of the SR peak and that of the LH peak. The SR trend was similar in both natural and CC cycles. VR in spontaneous cycles declined to a periovulatory nadir and then increased. The patterns of VR in CC cycles were similar except that values were initially depressed during and shortly after the end of CC therapy. Over 90% of VR increases were on the day of the LH peak and the day following. Results indicate that the method is useful for predicting ovulation in natural and CC cycles. Since the number of days by which ovulation is predicted exceeds the expected lifespan of spermatozoa in the female reproductive tract, the method also shows potential for use in natural family planning.