To date, it is not known whether the seasonal occurrence of sexual behavior and mating in free-ranging Hanuman langurs at Ramnagar, Nepal, is correlated with seasonal changes in female ovarian function, and, if so, which factor(s) triggers the onset of the reproductive period. Using noninvasive fecal hormone analysis in combination with behavioral observations, this study was carried out to: 1) investigate and characterize seasonal patterns of ovarian cyclicity and timing of conception in wild langur females living in a highly seasonal habitat; and 2) examine the relationship between seasonal patterns of ovarian cyclicity, behavioral estrus, and female physical condition. Behavioral data and fecal samples were collected during a total period of 14 months from nine females living in a multimale group. Physical condition of the females was assessed monthly by visual inspection, using a seven-fold scale. Ovulatory cycles and timing of conceptions were identified by the measurement of immunoreactive pregnanediol glucuronide (iPdG) in extracted feces. Hormone profiles in individual females revealed a clearly seasonal distribution in the occurrence of ovulatory cycles, which were restricted to the period from July to October. The distribution of female estrus behavior showed a similar seasonal pattern, and in total 88.2% of all estrus periods observed in the focal females were accompanied by ovulation. Onset of ovarian cycles as well as mating activities were strongly correlated with the onset of the rainy season. Females conceived, on average, in their second ovulatory cycle (pregnancy length: 211.6 ยฑ 3.4 days), with timing of conception being confined to the months when animals showed an improved physical condition. Collectively the present data clearly suggest that in seasonally-breeding langurs at Ramnagar, ecological conditions (rainfall, food availability, and quality) influence the onset of ovulations and timing of conceptions. Am.