The intravenous administration of 1 mg of: cortisol, cortisone, estradiol or progesterone, or the infusion of 5 i.u./kg body weight/24^h of thyroid stimulating hormone, had a facilitating effect upon fungus growth on the freshwater teleost Catostomus commersonii commersonii Lacépéde. The same dose (1 mg) of corticosterone or testosterone or adrenocorticotrophin (5 i.u./kg/24^h) did not have this facilitating effect.

The possible role of steroids in the mechanism of action of temperature in promoting infections in fish is discussed.