Protein-energy malnutrition is seen in patients with advanced stages of chronic kidney disease (CKD) and is even more pronounced in patients receiving long-term hemodialysis treatment. Both entities have great impact on patient morbidity and mortality. Analysis of body composition is an integral part of nutritional assessment and includes the estimation of muscle, fat, and fat-free mass, as well as the extracellular water compartment. Clinical assessment of these compartments is difficult, and gold-standard methods such as tracer dilution, magnetic resonance imaging, and dual-energy x-ray absorptiometry are expensive, cumbersome, and rarely available. We report an ongoing study of body composition in hemodialysis patients involving deuterium and sodium bromide dilution, total body potassium counting, magnetic resonance imaging, whole-body and segmental bioimpedance spectroscopy, and anthropometry. The goals of the study are (1) to validate bioimpedance technology against gold-standard methods for assessment of the various body compartments, (2) to directly quantify visceral adipose tissue mass, a potential source of cytokine production (adipokines) promoting chronic inflammation, and to study its relation to inflammatory markers, and (3) to directly quantify visceral organ mass and to study its relation to uremia toxin generation as assessed by protein catabolic rate and resting energy expenditure. Preliminary results based on up to 40 hemodialysis patients are reported.