We evaluated the way in which duration of hemodialysis treatment affects nutritional status in 96 end-stage renal failure patients. According to the length of previous hemodialysis treatment patients were divided into the groups: onset hemodialysis (ON-HD), early-stage hemodialysis (ES-HD, 1-8 months), mid-stage hemodialysis (MS-HD, 9-69 months), and advanced-stage hemodialysis (AS-HD, 70-207 months). Nutritional status was assessed by laboratory data (serum proteins, total lymphocyte count), intradermal skin antigen testing, anthropometric measurements (body mass index [BMI], infrared interactance), and records of food intake. ON-HD patients on a low-protein diet exhibited abnormally low values for serum total protein, albumin, transferrin, and total lymphocyte count and a high prevalence of anergy to skin antigens (69%). In the ES-HD and MS-HD groups values for serum proteins and total lymphocyte count were in the normal range and significantly higher than in ON-HD patients. In addition, a lower proportion of cutaneous anergy was observed (50% and 27%, respectively). Long-term hemodialysis therapy for 6-17 years (AS-HD) was associated with normal levels for all measured serum proteins. Subnormal levels of total lymphocyte count, significantly lower than in MS-HD patients, were associated with an increase in anergy to skin antigens (46%). Serum prealbumin, complement C3c, BMI, body fat, and lean body mass exhibited normal values in all patients and showed no differences between groups. These results indicate that diminished visceral protein stores, lymphopenia, and anergy to skin antigens are widespread in undialyzed uremic patients with end-stage renal failure but become uncommon after the initiation of regular hemodialysis therapy.(ABSTRACT TRUNCATED AT 250 WORDS)