The various symptoms and effects of ulcer disease are described and discussed. Data on the relative susceptibility of various species and age groups of trout are presented, as well as data concerning the methods of infection, rate of progress, and incubation period of the disease. Experimental evidence is given on the problem of healthy appearing fish which act as carriers of the disease. The effect of a number of drug treatments has been studied. An experiment was performed to determine the effect of diet and vitamins on the resistance of trout to the disease.