Increasing attention has been paid recently to the problem of protein and energy malnutrition and its effects on mortality and morbidity in hemodialysis (HD) patients. Protein deficiency has received more attention than other nutritional problems, largely because its consequences are more easily measured and large population studies have demonstrated the adverse effects of even small decreases in serum albumin on patient's survival. This review discusses these findings and presents other indicators of early malnutrition, which range from static measurements of plasma constituents such as transferrin and insulin-like growth factor 1 (IGF-1), kinetic measurements of protein catabolic rate (PCR) derived from urea kinetic modeling, and noninvasive measurements of body composition. In addition, the predialytic and dialytic factors that influence nutritional status, including the adverse effects of uremia, inadequate dialysis, membrane bioincompatibility, and intercurrent illness requiring hospitalization, as well as socioeconomic factors, are discussed. While some of these are difficult to deal with, the review emphasizes simple interventions that are likely to benefit the patient, including the delivery of optimal dialysis, appropriate choice of medications, and dietary interventions. Once malnutrition is established, parenteral nutrition may reverse the objective evidence of malnutrition, but its effects on survival have not yet been documented. Finally, the review addresses the effects of therapeutic substances such as growth hormone (GH) and erythropoietin (EPO) in combination with nutrients that at present appear to be favorable but are still being evaluated.