Protein malnutrition occurs in 41%-42% of peritoneal dialysis (PD) patients, indicating that the current intake of protein is inadequate in many patients. With an intake of protein > or = 1 g/kg/day, most continuous ambulatory peritoneal dialysis (CAPD) patients are in positive or neutral nitrogen balance, while with an intake below this there is considerable risk of negative nitrogen balance. Most CAPD patients are prescribed a diet containing 1.2 g/kg/ day protein or higher, yet the majority of patients have an intake lower than this. Several factors are associated with inadequate protein intake including older age, comorbidity, and loss of residual renal function when the dialysis regimen is inadequate. A minimum weekly Kt/V of 2.0 is needed to achieve a protein intake of 0.9-1.0 g/kg/day. Patients with peritonitis and a permeable membrane have increased losses of protein via the dialysate, and so are at risk for protein malnutrition. To prevent and treat protein malnutrition, routine assessment of both nutritional status and dialysis adequacy are needed. Patients with an adequate clearance (weekly Kt/V of 2.0 or higher, creatinine clearance of 60 L/week/1.73 m2), who are eating 1 g/kg/day and have no markers of malnutrition, including a normal serum albumin, require no intervention. Protein supplements can be prescribed to increase the protein ingestion to 1.2 g/kg/day or more, if the serum albumin is low, or if the patient is clinically malnourished with weight loss and decreased muscle mass. Gastro-paresis and esophagitis, common in PD patients, can be treated. If supplements, dietary counseling, and adequate dialysis regimen do not result in improvement of nutritional status, amino acid dialysate may be beneficial. One to two exchanges per day using amino acid dialysate converts the nitrogen balance from neutral to positive in malnourished CAPD patients. To use amino acid dialysate successfully, the physician must be sure that the clearance is adequate as the serum urea nitrogen rises; inadequate dialysis can result in uremia and decreased intake.