A bacterial exotoxin neutralization response by fish EgM antibody has not been demonstrated previously in any fish species. Channel catfish, Ictalurus punctatus, were immunized intraperitoneally with alum-adsorbed tetanus toxoid. Catfish immune serum demonstrated 1.28 antitoxin units (a.u.) of antitoxin neutralization and gave an indirect haemagglutination (IHA) titre of 1:65,536. After 2-mercaptoethanol (2ME) reduction of immune serum, no antitoxin neutralization remained by an IHA serum titre of 1:4096 was present. After Sephadex G-200 gel filtration of the catfish immune serum, the 14S antibody gave 0.32 a.u./ml and an IHA titre of 1:256. The 7S antibody gave no antitoxin neutralization but an IHA titre of 1.512 was found. After 2ME reduction, neither the 14S or 7S globulins demonstrated antitoxin neutralization, but minimal IHA titres of 1:16 and 1:4, respectively, were still found. The catfish immune serum and the 14S and 7S globulins did not precipitate tetanus toxoid by immunodiffusion in 1% agar gel.