Polychlorinated biphenyls (PCBs) are environmental contaminants that cause a variety of health problems in exposed populations, including adverse reproductive effects in females. The present study examined the ability of two PCB congeners, PCB 126 and PCB 52, to disrupt reproductive function at the level of the pituitary gland in females. Specifically, the ability of PCBs 126 and 52 to alter pituitary luteinizing hormone (LH) secretion in response to the hypothalamic releasing factor gonadotropin-releasing hormone (GnRH) was assessed. Subcutaneous oil or PCB injections (PCB 126 or 52 at 200 or 400 μg/kg bodyweight) were administered to ovariectomized female rats at 1000h for 2 days prior to experiments. On the day of experiments, hourly blood samples were drawn from 1100 – 1600h for LH measurements. Pentobarbital was administered at 1130h to block endogenous GnRH release. Exogenous GnRH (50 ng/pulse) or saline pulses were administered once every 30 min from 1200h-1530h. LH measurements revealed dose-dependent effects of PCBs 126 and 52 on GnRH-stimulated LH secretion, with the lower dose of PCBs inhibiting GnRH-stimulated LH secretion, and the two-fold higher dose enhancing GnRH-stimulated LH secretion. These results indicate that PCBs 126 and 52 alter pituitary sensitivity to GnRH, and provide evidence of yet another mechanism whereby PCBs interfere with reproductive function in females.