This prospective cohort study assesses the effects of exposure to organophosphate (OP) pesticides on adverse reproductive outcomes in both male and female agricultural workers in China. We will enroll women and their spouses, who are attempting to become pregnant, and observe reproductive endpoints including (1) semen parameters (concentration, total count, motility, progression and morphology), (2) menstrual disorders (oligomenorrhea, amenorrhea, polymenorrhea, intermenstrual bleeding, prolonged menstrual bleeding, dysmenorrhea, and irregular menstruation); (3) alterations in hormone patterns including reduced estrogen excretion (REE), anovulation, abnormal luteal phase (ALP), and abnormal follicular phase (AFP) in women and abnormalities of LH, FSH, TSH, SHBG, inhibin-B and testosterone in men; (4) fecundability; and (5) pregnancy outcomes including spontaneous abortion, preterm delivery, low birth weight, and intrauterine growth retardation.