Effects of acute poisoning of mercury compound and cadmium on the lactate dehydrogenase isozyme patterns in various tissues of goldfish, Carassius auratus, were studied by cellulose acetate electrophoresis. The LDH isozyme bands in brain, eye, muscle, liver, and intestine of normal fish were 3, 3, 3, 3 and 2 respectively, and decreased to 2,1,1 and 1 respectively except intestine under exposure to cadmium. The effect of cadmium on the LDH isozymes was stronger than that of mercury pollutant in the goldfish.