The optimum temperature for growth of juvenile walleyes (Stizostedion vitreum) was estimated by rearing fish under a low light intensity (i.e., 5 lx). The upper lethal temperature was estimated by slowly raising the acclimation temperature 0.5 C/d until death occurred. The estimates of 26 C and 34.1 C, respectively, were similar to those observed for juvenile walleyes in outdoor experimental channels, but were higher than those determined in the laboratory by one of the present authors for Minnesota walleyes. Some possible sources of error include the light intensity differences between experiments, which can influence predator-prey interactions (ration levels) in laboratory tanks, and the methods of fish acclimation to lethal temperature.