Various drugs were evaluated as regards efficacy for the treatment of Hexamita s a h o n i s infection in rainbow trout. The results confirm the efficacy of nitroimidazoles: infection was completely eradicated not only by metronidazole (which has been recommended previously for the treatment of hexamtosis), but also by benznidazole, ronidazole and secnidazole, which have not been assayed previously. The non-nitroimidazoles albendazole, amnosidine, hethylcarbamazine and nitroscanate also completely eliminated infection. The remaining non-nitroin~idazoles tested (amproliun~, bithionol, febantel, flubendazole, levamisole, netobimin, niclosamide, nitroxynil, oxibendazole, parbendazole, piperazine, praziquentel, tetramisole, thiophanate, toltrazuril, trichlorfon and triclabendazole) were not effective KEY WORDS. Hexamitosis . Ranbow trout. Treatment Drugs