Cold-exposed male Sprague-Dawley rats were forced to obtain their extra caloric requirements from either carbohydrate (sucrose) or fat (Crisco). Rats were killed, one, four and eight weeks after initiation of the feeding regimen. Carcass fat, protein, and moisture analyses were made. Liver glucose-6-phosphatase (G-6-Pase), hexose monophosphate (HMP) dehydrogenase, and glycogen were assayed. At the end of four weeks and eight weeks the percentages of fat in the carcasses of these rats were significantly higher than in the cold-exposed rats receiving a mixed complete diet ad libitum. The two enzymes studied showed differing responses, HMP dehydrogenase increasing as a result of higher input of carbohydrate in the cold, and G-6-Pase increasing as an apparent result of cold exposure per se.