A group of carp were immunized with bovine serum albumin. The fish, kept at low temperature (12°) after initially being kept at high temperature (25°) for a short period following the first antigen stimulation, showed a rising titre of antibody. In contrast no circulating antibody was found in carp kept at 12°. This rising titre occurred whether they were transferred to low temperature before or after appearance of first circulating antibodies. The anamnestic response which occurred in carp kept at high temperature may also take place, under certain conditions, at low temperature.