The authors explored whether exposure to 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its isomers and metabolites affects female reproductive hormones characterized by urinary pregnanediol-3-glucuronide (PdG) and estrone conjugate (E(1)C) levels. During 1996-1998, 287 newly married Chinese women nonsmokers intending to conceive were prospectively studied. Serum for DDT measurement was collected at enrollment, and daily menstrual diaries and urine specimens were collected for 1 year or until a clinical pregnancy was achieved. More than 500 menstrual cycles were studied totaling over 8,000 days. Day of ovulation was determined for each cycle, and the association of serum DDT levels with daily PdG and E(1)C levels in a +/-10-day window around ovulation was analyzed. After adjustment for covariates including age, body mass index, and occupational exposures, consistent inverse associations of most DDT forms occurred with urine E(1)C during the periovulation phase and with urine PdG during the luteal phase of the menstrual cycle. For example, a 10-ng/g increase in serum p,p'-DDE was associated with a 0.05-log(E(1)C) decrease (p = 0.03) in the periovulation phase and a 0.06-log(PdG) decrease (p = 0.03) in the luteal phase. These results support the potential for DDT to be associated with decrements in estrogen and progesterone levels at times during the menstrual cycle that are critical for ovulation and early pregnancy maintenance.