Radio-thyroidectomized (TX) goldfish, and goldfish treated with adreno-corticotropic hormone (ACTH), thyrotropic hormone (TSH) or thiourea were initially acclimated to 1 of 4 temperatures (30[degree]C, 25t, 15[degree]C, or 5[degree]C). After 3 weeks at the initial acclimation temperature the fish were transferred to one of the other temperatures and the pattern of acclimation to the new temperature was followed by measuring oxygen consumption. A period of 12 hr. was allowed in bringing the fish from one temperature to the other. Oxygen consumption measurements were taken daily for the first 5 days following the transfer and at intervals of 2 or 3 days thereafter. The metabolic effect of sudden brief exposures to different temperatures was also measured in TX and ACTH-treated fish acclimated to 30[degree]C, 15[degree]C, and 5[degree]C. Acclimation patterns of the treated animals did not differ significantly from those of controls having the same thermal history suggesting that the thyroid and adrenal glands are not directly involved in the temperature acclimation processes of goldfish. Acclimation to low temperature showed less metabolic compensation and appeared to be completed sooner than that to high temperature.