Endocrine changes during early pregnancy have been studied in 12 patients between days 35 and 91 from the last menstrual period. Ovulation had occurred spontaneously in five patients and was induced with clomiphene citrate (CC) in the remaining seven women. All the patients collected daily samples of early morning urine throughout the period of study; on each sample, human chorionic gonadotropin (hCG), pregnanediol-3-alpha-glucuronide (PGDG) and estrone-3-glucuronide (E1G) were measured by chemiluminescence immunoassay. No significant difference was observed between the two groups of patients with respect to the concentrations of hCG and PGDG. The excretion of E1G, however, was significantly higher in patients treated with CC. These data suggest that the induction of ovulation with CC may affect estrogen production in early pregnancy.