Cyclic AMP and cyclic GMP daily excretion was measured in urine using specific radioimmunoassays, during 12 normal menstrual cycles. Wide day to day variations for both nucleotides were observed. In 6 out of the 12 women, an elevation of urinary cyclic AMP excretion occurred around the ovulatory phase, paralleled by cyclic GMP in 5 cases. Urinary cyclic GMP was higher during the second phase of the cycle in 10 out of 12 women. Daily variations of urinary cyclic AMP and cyclic GMP measured over a long period did not appear to be associated.