In order to assess the efficacy of selected aromatase inhibitors on Atlantic salmon (Salmo salar) ovarian and brain tissue, in vitro systems were developed for measuring 17߭estradiol (E2) production by these tissues. Isolated vitellogenic follicles, or homogenised whole brains were incubated at 10 àin complete Cortlands solution for 18 or 42 h respectively, and E2 levels in themediumwere determined byRIA. The addition of testosterone to the medium increased E2 production in all preparations. E2 production by whole brain homogenate was reduced by co-incubation with the aromatase inhibitors 1,4,6-androstatriene-3,17-dione (ATD), 4-androstene-4-ol-3,17-dione (OHA), aminoglutethimide, fadrozole or miconazole. Fadrozole, ATD, and OHA reduced E2 production by vitellogenic follicles at a medium concentration of 0.1 姠mL-1, whereas miconazole was only effective at 10 姍 mL-1. This study demonstrates a simple and rapid screening method for assessing the efficacy of aromatase inhibitors on fish tissues, and that the aromatase inhibitors ATD, OHA and fadrozole are potent inhibitors of both brain and gonadal aromatase in vitro, in Atlantic salmon.