A wide variety of chemicals discharged from industrial and municipal sources have been reported to disrupt the endocrine system of animals, which may be exposed via the food chain and contaminated water. 17α-Ethinylestradiol (EE(2)), a drug used in oral contraceptives and hormone replacement therapy, has a widespread presence in the aquatic environment. Current knowledge on the sensitivity of marine fish to estrogenic environmental chemicals is limited. We report here the effects of dietary intake of EE(2) on gilthead seabream, a marine hermaphrodite teleost, focusing on the immune events that take place in the gonad. When seabream males were fed with 5, 50, 125 and 200μg EE(2)/g food for 7, 14, 21 and 28days an infiltration of acidophilic granulocytes and B lymphocytes occurred in the testis as the same time that spermatogenesis is disrupted. Moreover, the dietary intake of EE(2) promoted a dose-dependent up-regulation of the expression of genes coding for cytokines, chemokines and adhesion molecules correlated with a leukocyte infiltration. Copyright © 2011 Elsevier Ltd. All rights reserved.