A new rapid and simple method is introduced to measure subcutaneous fat and evaluate total body fat. It is based on real-time ultrasound and requires equipment that is used in routine examination of subcutaneous structures, e.g., thyroid gland. Results from seven regions of skin in 100 subjects correlated well with total body weight, Broca's index, and deviation from average weight 0.02 greater than P greater than 0.001). Comparisons were also made with measurements of subcutaneous fat from skinfolds. There was an excellent correlation of values (P less than 0.001 in all experiments), although ultrasound results tended to be slightly higher. For calculation of total body fat, ultrasound values were converted by regression equations to "calculated skinfold thickness"; when applying established mathematical models for calculating body fat from skinfold thickness results were equal in both methods (P greater than 0.1).