The primary objective of this research is to develop a new method for measuring basal body temperature (BBT) that can become a reliable basis for detecting ovulation. This method must be more accurate intrinsically as well as in application. Phase I demonstrated the feasibility of this objective by using freshly-voided urine as the site and a newly designed and fabricated liquid crystal thermometer. Phase I also indicated that to optimize the accuracy of the urinary BBT measurements, further refinements in the thermometer and collection vessel were necessary. The development of these refinements and the execution of a field trial engaging 50 women through four menstrual cycles using the final urinary device are the principle aims of the Phase II research. Measurements using the conventional oral method to construct BBT charts will be taken for comparison. The timing of the thermal events on these charts will be assessed relative to the hormonal standard for ovulation detection. The purpose of this trial is to demonstrate that BBT charts obtained using the urinary method can be used to identify the thermal events which bracket ovulation with greater accuracy than is presently possible with the oral method. If these aims are achieved, women will have a simple, inexpensive, safe and effective method for detecting ovulation and using that information for either contraception or infertility treatment.