Endometriosis is a chronic disease affecting ~15% of US reproductive-aged women, and is a significant cause of infertility. One suggested risk factor is exposure to organochlorines (OC). Diagnosed cases of endometriosis have been detected with longer exposure or higher serum concentrations than controls for OCs (PCDD, PCDF, and PCB/dioxin); however, study results have been inconsistent due partly to small numbers of cases/controls and limited exposure history. Analyses using the Agricultural Health Study will provide a significantly larger sample size for a case-control study and detailed measures of pesticide and environmental exposure to common agricultural pesticides and to these OCs. Study results will be used as pilot data for an National Institute of Child Health & Human Development (NICHD) proposal of clinic-based case-control study. In 2010, an NICHD Fertility Preservation Research Program, sought grants to characterize occupational and environmental exposures that may be associated with risks of infertility. This exposure and infertility issue continues to be of interest to NICHD.