Tissue and (or) chemical body composition was determined in 18 Svalbard reindeer, aged 1 1/2 mo. prepartum to 9 3/4 yr, and in mainland Norway reindeer, aged 1 1/2 mo. prepartum to 1 1/3 yr. At the end of the growing season, the fat content in the ingesta-free body was very high (27-40%) in Svalbard reindeer. Two mainland yearling males had 4.5% body fat as compared to 27.8% in a Svalbard male yearling. At the end of winter the weight decrease of Svalbard reindeer was close to 50%. The loss of ash, protein, water and fat from the body was estimated at 16.8, 30.9, 34.3 and 76.3%, respectively. Animals that had starved to death showed an additional weight loss of 8% and a nearly complete loss of fat. Liver content of Fe increased from 97 mg/kg in late summer to 3463 mg/kg in late winter and 5075 mg/kg in animals that had starved to death. There were significant linear relationships between the percent water and percent fat in the ingesta-free body, and between the weight of the fat-free and ingesta-free body and the weight of its components, i.e, water, protein and ash.