The aim of this study was to use measurements of urinary steroid glucuronides to confirm the suppression of ovulation of ovulation in women taking oral contraceptives. Urinary concentrations of oestrone-3-glucuronide (E1G) and pregnanediol-3 alpha-glucuronide (Pd-3-G) were measured by radioimmunoassay in early morning urine samples from six normally-menstruating women and six women who were taking combined oral contraceptives. In the normally-menstruating women, E1G concentrations, and the E1G/Pd-3-G ratio, increased 2-3 fold before ovulation. There was no midcycle increase in either measure in women taking oral contraceptives. We suggest that measurement of these steroid metabolites provides a means of assessing the anti-ovulatory effects of oral contraceptives.