The effects of various temperature shifts on the kinetics of the humoral antibody response in oliver flounder, Paralichthys olivaceus, immunised with formalin-killed Edwardsiella tarda, were determined by measuring the antibody production in vivo and in vitro. When fish acclimated to a high temperature and immunised at that temperature were transferred to a lower temperature (22℃ to 12℃) at a various times after immunisation, the fish showed a weaker immune response than that achieved when the fish were kept at a high environmental temperature. However, in the converse experiment (12℃ to 22℃), the magnitude of the humoral immune response was recovered independent of the time of the transfer after immunisation at low temperature, even though the peak levels of each transferred group did not reach the level found in the positive control group that was maintained and immunised at a high environmental temperature. Hence, these studies provide some evidence that the potential for antibody production in B cells of oliver flounder immunized at high temperature is not impaired by subsequent exposure to low temperature.