Information regarding the use of brightness-mode (B-mode) ultrasound for separately measuring the thickness of subcutaneous fat and skeletal muscle in the calf area was evaluated. Subjects were volunteers, 32 men and 32 women college students. Fat was measured with skinfold calipers and B-mode ultrasound. We used calf circumference and B-mode ultrasound simultaneously to assess muscle size. Ultrasonic measurements of both fat and muscle were repeated within 30 minutes to evaluate reliability. Men were 24 percent heavier than women but had a thinner fat layer as measured by skinfolds (49%) and ultrasound (29%). Men also had a relatively larger calf muscle as assessed by circumference (7%) and ultrasound (29%). Intraclass correlation coefficients were no less than .99 for repeated ultrasonic measurements of both fat and muscle for men and women; therefore, these procedures are reliable for at least a short period of time. Associations between skinfolds and fat sonograms were high in men (r = .87) and moderate in women (r = .50). Associations between circumferences and muscle sonograms were moderately high in both men (r = .80) and women (r = .76). All four associations were statistically significant (p less than .05).