One hundred grams of glucose with 50 microCi U-14C-glucose were given orally to 17 women with widely varying amounts of body fat. Radioactivity and glucose metabolism in vitro were then measured in adipose tissue obtained by needle biopsies in the abdominal and femoral regions after four hours. Radioactivity in triglycerides was then measured in repeated biopsies 1 day, 1 week, and monthly up to 7 months after glucose administration. Glucose label in triglycerides after four hours was higher in abdominal than femoral adipocytes in obese women. It increased slightly during the following week, and then decreased exponentially with a half-life of 12 months in the abdominal region and 19 months in the femoral region. Uptake of glucose carbon in total body fat was estimated from the triglyceride label measured and determinations of body fat mass, and found to be in the order of less than 4% of given glucose. The studies in vitro suggested that much of the glucose taken up in adipose tissue is converted to lactate. If this is the case in vivo, then glucose uptake in adipose tissue might well be of significance for total body glucose homeostasis, particularly in obese subjects, amounting to maximally perhaps one third to one half of the oral glucose given. The majority of this glucose uptake would then, however, leave adipose tissue again as lactate. The shorter half-life of label in abdominal adipocytes is in agreement with findings of increased lipolysis in these adipocytes in vitro.