Many persistent pesticides have been implicated in reproductive and developmental adverse effects, in man and wildlife. It has been hypothesized that these so-called xeno-hormones could upset the endocrine system function by binding to human estrogen receptor alpha and beta (ERα, β) and thus be responsible for the higher incidence of breast and cervical cancer, infertility and endometriosis. In this report, forty-nine pesticides were tested for ERα and β activation or inhibition in stable reporter cell lines, HELN ERα and ERβ. Stable transfection of the ERα and ERβ constructs together with an estrogen reporter luciferase vector into the HeLa cell line resulted in two estradiol-sensitive cell lines. In our model, fifteen of the tested pesticides were found to agonize the ERα-mediated transcription in a dose-dependent manner and DDT, trans-nonachlor, chlordane, fenvalerate and toxaphene were also capable to activate ERβ. Antagonistic activities toward hERα and hERβ were shown in three (carbaryl, pentachlorophenol and 2,4,5-trichlorophenoxyacetic acid) and seven (chlordecone, methoxychlor, carbaryl, endosulfan, endrin, dieldrin, aldrin) pesticides, respectively. Remarkably chlordecone and methoxychlor which were the most effective antagonist compounds for hERβ, were agonists for hERα. Although the ERα activation potential of the pesticides was lower than that of estradiol, the overall body scale response might be amplified by the ability of pesticides to act via several mechanisms and by frequent and prolonged exposure to different pesticides, even at low concentrations.