Objective: Prospective evaluation of the effect of 6-month-long intradialytic amino acids (AA) supplementation on selected nutritional variables in malnourished hemodialysis (HD) patients. Design: Multicenter, prospective, (nonrandomized, noncontrolled) observational study. Setting: Thirty-one HD units affiliated with academic centers and tertiary-care hospitals. Patients: Adult patients treated by HD for at least 6 months. Inclusion criteria were: serum albumin concentration : 39 g/L and at least 4% loss of body weight during the last 6 months in otherwise stable HD patients. From a cohort of 133 patients who were enrolled, 97 (54 men and 43 women) were eligible for the analysis. Intervention: Intradialytic AA supplementation with 500 mL 10% solution per HD session for a period of 6 months. Main Outcome Measures: Serum albumin concentration, modified Subjective Global Assessment (SGA) score, body mass index (BMI), mid-arm circumference (MAC), and total lymphocyte count. Measurements were recorded at baseline and after 3 and 6 months of AA supplementation. Results: Serum albumin concentration increased significantly from the mean 32.5 +/- 4.6g/L at baseline to 36.4 +/- 4.8 g/L at 3 months (P <.001) and 37.1 +/- 4.8g/L at final observation (P <.001 versus baseline). Significant correlation was observed between frequency of AA supplementation and serum albumin increase (r = 0.41; P <.0001). Rate of improvement negatively correlated significantly with baseline concentration of serum albumin (r = -0.42; P <.0001). SGA score significantly improved from median of 16 points at baseline to 12 points at 3 months (P <.01) and 11 points at 6 months (P <.01 versus baseline), and this improvement also correlated with the frequency of AA supplementation. Small yet significant increase of MAC was observed at 6 months (from baseline 24.1 +/- 4.3 to 24.8 +/- 4.8 cm; P <.01), whereas BMI remained unchanged. Conclusion: Intradialytic AA supplementation improves selected nutritional parameters of HD patients with malnutrition. The improvement depends on the intensity of supplementation. (C)2004 by the National Kidney Foundation, Inc.