D u r i n g a 2-year study of the ecology of barren-ground car ibou (Rangifer tarandus groenlandicus) on Coats Island, N o r t h w e s t Territories , Canada , 27 side dissections were conducted; bone, muscle, and fat were separated and weighed. Mature female caribou made up 17 of the 27 dissections and the remaining 10 were calves ranging i n age f r o m 1 week to 11 months. The extreme cycle of body condi t ion in Coats Island car ibou permitted the study to span the range f rom fat fall animals to emaciated spring animals near starvation. Weight of the gastrocnemius muscle (a small , readily identifiable muscle in the h i n d quarter) was an accurate predictor of total muscle weight ( In (total muscle in kg) = —2.791 + 1.071 In (gastrocnemius weight in g); r = 0.98). The regression was not affected by age or cond i t ion , and muscle compos i t ion varied little w i t h season except in very lean animals, in w h i c h intramuscular fat decreased. Weight of the femur was an equally useful predictor of total bone weight (In (total bone in kg) = —4.878 41.137 In (femur weight in g); r = 0.98). This regression was also unaffected by age or cond i t ion . Three carcass fat depots — subcutaneous, intermuscular, and pelvic — and two internal depots — omental and perirenal — were graphed against the total fat in these depots for each animal. Age and body condi t ion again had little effect on the curves for each depot. Subcutaneous fat was the latest maturing but the earliest depleted. A multiple Rangifer, Special Issue N o . 1, 1986: 353