Uronic acid (UA) content in whole urine showed a characteristic pattern of fluctuations during menstrual cycle (24 cycles) with a distinct peak on the day of ovulation (midcycle peak 1043 + 68 micrograms/ml urine. This peak of maximal UA concentration was validated by ultrasonography (abdominal and/or vaginal scanner and basal body temperature. In hormonal induced menstrual cycle (5 cycles) a significant decrease in Ua concentrations were observed during the follicular phase (20%) and in the midcycle peak (11%) when they were compared with the same values in the normal cycle. Nevertheless, two days after the ovulation peak occurs a second peak can be observed (1344 + 799 micrograms UA/ml urine). On the other hand in the anovulatory cycles (5 cycles) the same diminishing behavior in the UA concentrations were observed in both phases of the cycle (50-60%) with the expected lack of the midcycle peak. Results that clearly show that UA excretion in urine reflect a excellent correlation with the menstrual cycle allowing us to propose this technique as an accurate and reliable method to detect ovulation.