Dichlorodiphenyltrichloroethane (p,p ' DDT) is an endocrine-disrupting chemical (EDC). Several studies showed an association between p,p ' DDT exposure and reprotoxic effects. We showed that p,p ' DDT was a positive allosteric modulator of human follitropin receptor (FSHR). In contrast, we demonstrated that p,p ' DDT decreased the cyclic AMP (cAMP) production induced by human choriogonadotropin (hCG). This study evaluated further the effects of p,p ' DDT on Gs-, beta-arrestin 2- and steroidogenesis pathways induced by hCG or luteinizing hormone (LH). We used Chinese hamster ovary cells line stably expressing hCG/LHR. The effects of 10-100 mu M p,p ' DDT on cAMP production and on beta-arrestin 2 recruitment were measured using bioluminescence and time-resolved resonance energy transfer technology. The impact of 100 mu M of p,p ' DDT on steroid secretion was analysed in murine Leydig tumor cell line (mLTC-1). In cAMP assays, 100 mu M p,p ' DDT increased the EC50 by more than 300% and reduced the maximum response of the hCG/LHR to hCG and hLH by 30%. This inhibitory effect was also found in human granulosa cells line and in mLTC-1 cells. Likewise, 100 mu M p,p ' DDT decreased the hCG- and hLH-promoted beta-arrestin 2 recruitment down to 14.2 and 26.6%, respectively. Moreover, 100 mu M p,p ' DDT decreased by 30 and 47% the progesterone secretion induced by hCG or hLH, respectively, without affecting testosterone secretion. This negative effect of p,p'DDT was independent of cytotoxicity. p,p ' DDT acted as a negative allosteric modulator of the hCG/LHR signalling. This emphasizes the importance of analyzing all receptor-downstream pathways to fully understand the deleterious effects of EDC on human health.