Specific polyclonal antibodies against the two salmonid gonadotropins (GTHs) were developed using two synthetic oligopeptides corresponding to GTH Iβ-(96–113) and GTH IIβ-(107–119), respectively. By Western blot analysis under reducing conditions, anti-GTH Iβ-(96–113) detected one specific band corresponding to GTH Iβ (17 kDa) and anti-GTH IIβ-(107–119) detected one specific band corresponding to GTH IIβ (20 kDa). Neither antibody recognized bands under nonreducing conditions. By immunohistochemical analysis, immunoreactive (ir-) Iβ-(96–113)-and ir-IIβ-(107–119)-cells had different regional distributions among the aldehyde fuchsin positive cells and were not stained with an anti-human thyrotropin β antibody. In salmonid fishes (chum salmon, rainbow trout, brook trout, whitespotted char, dolly varden and huchen), each antibody reacted with distinctly separate hypophyseal cells. However, in nonsalmonid species, and even in the salmoniform fish, the ayu (Plecoglossus altivelis), no pituitary cell was stained with these antibodies. These data indicate that these antibodies are useful tools for studying the change and the function of GTHs in salmonid fishes.