The oxygen consumption of brain, liver and gills excised from goldfish (Carassius auratus) adapted to 30[degree]C or 10[degree]C was measured at various temperatures between 10[degree] and 30[degree]. Rate-temperature curves revealed no significant differences between brain or between liver homogenates from 10[degree]- or 30[degree]- adapted fish. However, the Q02 of gills (whole or homogenized) from fish adapted to 10[degree] was significantly higher than the QO2 of gills from 30[degree]- adapted fish. A seasonal variation independent of the temperature of adaptation (higher QO2 in summer than during winter months) was also noted for whole gills. Inhibition of oxygen consumption (measured at 26[degree]) by 10"3 m cyanide or 5.4 x 10-4 [image] iodoacetate disclosed that gills from 30[degree]- adapted fish were significantly more resistant to cyanide and significantly less resistant to iodoacetate than were gills from fish adapted to 10[degree]. These results suggest that the cytochrome system has become less sensitive to cyanide poisoning or that an alternate pathway less sensitive to cyanide than the cytochrome system has increased in activity in gills from fish adapted to 30[degree], and that the hexosemono-phosphate shunt may be more active in gills from 10[degree]- adapted fish.