Subcutaneous fat thickness of 26 young males (aged 18-32 years) was measured at eight sites (biceps, triceps, subscapula, axillary, subcosta, paraumbilica, suprailiaca, quadriceps) using a commercial high-resolution B-scan ultrasound equipment with a 7.5-MHz transducer as well as a Holtain skinfold caliper. The aim of the study was to investigate the relationship between ultrasound and skinfold caliper measurements of subcutaneous fat and body density determined by the hydrostatic weighing technique. Correlations between ultrasound and caliper measurement were above 0.7. The variability of duplicate measurements with the skinfold caliper appeared to be somewhat lower than with ultrasound measurements. Using all possible subsets regression, for both techniques measuring subcutaneous fat thickness those multiple regression equations were chosen which predicted body density best. The best equations for the two techniques explained about 80 percent of the variance of body density in this group. These results indicate that in young men, body fat can be estimated with the same degree of accuracy using either the skinfold caliper or the ultrasound technique, but for estimates of actual subcutaneous fat thickness, ultrasound is to be preferred.