The effects of adenosine (ADO) and adenine (ADE) on cold acclimation were studied in mice of the ddY strain. At 5 weeks of age, mice were maintained at 4 degrees C for 4 weeks. Test groups of mice were supplied with a 0.05% (w/v) solution of ADO or ADE as drinking water in addition to water. We measured changes in body weight, intake of water and food, rectal temperature upon acute exposure to -20 degrees C, weight of interscapular brown adipose tissue (BAT) and the levels of glucose, nonesterified fatty acids (NEFA) and 3H-butyrate in the blood prior to and after exposure to the lower temperature of -20 degrees C. Chronic exposure to cold (4 degrees C) reduced body-weight gain for the first two weeks but weight gain recovered within the next two weeks. ADO partially but selectively inhibited the gain in body weight. This effect was marked in mice maintained at room temperature. Such an inhibitory effect was the case of ADE in the room temperature. Exposure to cold stimulated the daily consumption of food. ADO further and selectively enhanced food intake, but ADE enhanced that in room temperature. Cold increased in daily intake of water. Both ADO and ADE accelerated the intake of water. This effect was marked in mice maintained at 4 degrees C and the effect of ADE was considerable. Mice chose to drink the water that contained ADO, while the choice of water that contained ADE was apparent only during exposure to cold. Exposure to cold rendered mice resistant to severe cold (-20 degrees C). ADO and ADE partially reduced this resistance. Exposure to cold increased the weight of BAT but ADO selectively prevented this increase. Cold did not change the levels of the various compounds measured in the blood. In mice exposed to 4 degrees C for 4 weeks, acute exposure to severe cold decreased the glucose level and increased the levels of NEFA and 3H-butyrate. ADO selectively prevented the changes in the levels of NEFA and 3H-butyrate. It remains to be confirmed whether the growth of brown adipocytes is always necessary when mice acclimate to cold.