We studied the effects of gonadol steroid implants on catecholamine levels in the brain of ovariectomized female toadfish (Opsanus tau L.). Control values for dopamine (DA), norepinephrine (NE) and epinephrine (EPI) in the brain were 2181 +/- 226, 1112 +/- 80 and 6.5 +/- 2.02 ng/g, respectively. Compared to controls, 17 beta-estradiol decreased brain levels of DA to 547 +/- 261, and dihydrotestosterone decreased DA to 444 +/- 290 ng/g (P less than 0.001). Furthermore, dihydrotestosterone increased brain levels of EPI to 15.0 +/- 4.7 ng/g. The steroids had no effect on brain levels of NE. These results suggest a role for both androgens and estrogens in regulating brain levels of DA and EPI in toadfish.