Lipid and water together typically make up more than 90% of the body's adipose tissue mass. Although some reports have shown that the fraction of lipid in adipose tissue is greater in obese people than in lean ones, the quantitative relationship between adipose lipid fraction and overall adiposity of the body has never been investigated. We dissected six male unembalmed cadavers and weighed all adipose tissue (range 9.7-25.7 kg), allowing the calculation of percentage adiposity as 100 x total adipose mass/body mass (range 17.8-43.9%). Adipose tissue volume was determined by hydrostatic weighing of all portions of the dissected adipose tissue. For the six cadavers, whole body adipose tissue density ranged from 0.925-0.970 g/ml. Based on a three-component model of adipose tissue (lipid, water and dry fat-free solids), an expression for lipid fraction, F, was derived. After assuming densities for adipose lipid (0.905 g/ml), water at 36 degrees C (0.997 g/ml) and the dry fat-free component (1.38 g/ml), the equation simplified to F = 6.256/D-5.912, where D is adipose tissue density (g/ml). Lipid fraction was then calculated for each of the six cadavers: the range (0.54-0.85) was in excellent agreement with published data. There was a significant correlation (r = 0.95, P < 0.005) between calculated lipid fraction and percentage adiposity. The regression equation predicting lipid fraction from percentage adiposity was y = 0.327 + 0.0124x. We conclude that the estimated fraction of lipid in human adipose tissue shows both a wide range and a strong positive linear relationship with overall body fatness.