The effects of handling and anesthetization with tricaine methanesulphonate (Ayerst "Finquel") upon brook trout (Salvelinus fontinalis) have been investigated with reference to selected hematological and cardioventilatory parameters, and several aspects of body fluid chemistry. Alterations in hemoglobin, hematocrit, and total dissolved solids suggest that exposure to the anesthetic prompts a rapid hemoconcentration. Water content increases, and the plasma, tissue, and estimated cellular levels of several of the major electrolytes (sodium, potassium, calcium, and magnesium) are altered. Observations upon cardiac activity, dorsal aortic pressure, and ventilatory rate and amplitude support the hypothesis that Finquel exerts a depressive influence upon central autonomic functions. Handling alone leads to significant changes in plasma glucose and lactate levels, and in the concentrations and distributions of a number of the electrolytes investigated.