The adipose tissue volumes of 12 women were determined by computed tomography (CT). Body weight ranged from 46 to 129 kg. Nine or twenty-two transsectional scans were examined with respect to the adipose tissue area. The total adipose tissue volume (ATCT22 or ATCT9) was calculated by assuming linear changes in the adipose tissue area between adjacent scans. Body fat (BF) was also calculated from total body potassium (BF40K), from total body water (BFTHO), and from both these determinations (BF40K + THO). Body mass index (BMI) was calculated by dividing body weight (BW) by height2 (H2). ATCT22, ATCT9, and BFK were more closely related to BW and BMI than were BFTHO and BF40K + THO. When ATCT was used as a standard, the optimal index of adiposity based on BW and H was in the range BW/H0.8 to BW/H1.2. From the CT and 40K measurements it was possible to deduce that the potassium content is 62 mmol/kg fat free mass and 73-75 mmol/kg lean body mass. The error of ATCT9 was 0.6%, while that of BF40K was at least three to four times larger. It is concluded that the CT-based AT determination is the most reproducible method so far available. The technique might turn out to be of great value in human energy balance experiments.