Cellular temperature compensation of green sunfishLepomis cyanellus, a species active in cold water, was compared to that of the cofamilial smallmouth bassMicropterus dolomieui, a species quiescent in cold water. It was hypothesized that there would be a correlation between degree of cellular temperature compensation and degree of coldwater activity for these two centrarchids. Fishes were acclimated to 5, 15, or 25°C in the laboratory for 10 weeks. In both species, red muscle citrate synthase activity was elevated in fish acclimated to 5 and 15°C relative to those at 25°C. Red muscle area per body cross-sectional area was elevated in both species acclimated to 5°C relative to those at 25°C. Heart ventricle citrate synthase activity and ventricular weight showed temperature compensation in the smallmouth bass but not in the green sunfish. These data do not suggest a correlation between degree of cellular temperature compensation and degree of coldwater activity for these two centrarchids. Winter quiescence of smallmouth bass is almost certainly facultative, and cellular temperature compensation may commonly occur in facultatively quiescent ectotherms.