Sulfamerazine, sulfamethazine, sulfathiazole, and sulfamerazine alternated at 4‐day intervals with sulfathiazole, were compared in the treatment of furunculosis among yearling and fingerling brook trout at the Leetown Station of the U. S. Fish and Wildlife Service, Kearneysville, West Virginia, in 1947. The daily dosage rates were: for sulfamerazine and sulfamethazine, 6 grams per 100 pounds of fish (13.2 grams per 100 kilograms); for sulfathiazole, 12 grams per 100 pounds. The drugs were mixed thoroughly with the food.

The courses of the epizootics were very different in the two age groups. With yearlings, mortalities were as follows: controls, 100 percent; sulfathiazole, 75 percent; sulfamethazine, 62 percent; sulfamerazine‐sulfathiazole, 43 percent; sulfamerazine, 29 percent. With fingerlings, treatment was initiated sooner after the onset of the disease. Although mortality was finally heavy in the fingerling control, sulfonamide therapy was very much more effective and losses correspondingly less severe. Mortalities were as follows: controls, 90 percent; sulfathiazole, 11 percent; sulfamerazine, 8 percent; sulfamerazine‐sulfathiazole, 6 percent; sulfamethazine, 5 percent.

Sulfathiazole was markedly inferior to sulfamerazine. Sulfamethazine showed sufficient promise to warrant further trial. Sulfamerazine still seems the best for an acute infection and the drug most suitable for the treatment of furunculosis in brook trout.

Important was the revelation of the extreme difference in the courses of the epizootics and the apparent correlation of effectiveness of treatment with the type of epizootic. However, prompt initiation of treatment may largely explain the great effectiveness of the various drugs with the fingerlings.