1,1-Dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), a metabolite of DDT (1,1-dichlorodiphenyltrichloroethane), is a persistent hormonally active environmental toxicant that has been found in human serum and follicular fluid. The objective of this study was to determine whether DDE can alter free calcium ion concentrations in the cytosol ([Ca² ]_cyt) of human granulosa cells. Changes in [Ca² ]_cyt in single cells loaded with Fura-2 were studied using a dynamic digital Ca² imaging system. At a concentration of 100 ng/ml, DDE stimulated small elevations of [Ca² ]_cyt accompanied by Ca² oscillations. At 1 μg DDE/ml, there was a biphasic Ca² response with marked elevations of [Ca² ]_cyt over time. In Ca² -free medium, cells showed an initial small elevation of [Ca² ]_cyt, which was magnified after addition of Ca² to the medium. Washing the cells after DDE treatment failed to remove the elevated [Ca² ]_cyt and oscillations, both of which were eliminated by addition of EGTA. ATP also induced [Ca² ]_cyt elevations and oscillations, and these effects were potentiated when DDE was added. FSH induced transient [Ca² ]_cyt elevations, whereas hCG caused a prolonged elevation and marked oscillations in [Ca² ]_cyt. These results suggest that DDE at concentrations normally found in human tissues induces elevations in [Ca² ]_cyt in granulosa-lutein cells. Our data therefore highlight a novel mechanism through which DDE can alter endocrine homeostasis and possibly act as an endocrine toxicant.