We studied normalized urea nitrogen appearance (NUNA), normalized protein catabolic rate (NPCR), and normalized daily creatinine excretion (NDCE) in twenty-one patients (15 men, 6 women; mean age 63 +/- 9 years) on CAPD for more than 4 years (80 +/- 27 months). In the same patients we evaluated the changes in serum albumin and transferrin with time. After 74 +/- 26 months on CAPD, NUNA was 0.12 +/- 0.03 g/Kg IBW/day, NPCR = 1.09 +/- 0.19 g/Kg IBW/day; NDCE = 15.1 +/- 3.1 mg/Kg IBW/day; serum albumin = 3.8 +/- 0.2 g/dl. NUNA was correlated with NPCR (p < 0.001) and both were correlated with NDCE (p = 0.007 and p = 0.008). NPCR significantly decreased as patient age increased (p = 0.007) but was not correlated with time on CAPD, sex or serum albumin. Serum albumin did not change as age increased. Serum albumin and serum transferrin had not significantly changed after 4 years (after 8 years in a subgroup of eight patients). Finally, we compared these data to the initial data recorded for the same patients (mean interval: 64 +/- 21 months). NUNA, NPCR and NDCE did not change significantly. Changes in NPCR were directly related to changes in NDCE (p = 0.019). This study supports that long-term CAPD does not necessarily impair nutritional status and suggests that the oldest patients can maintain stable serum albumin concentrations on lower protein intake than younger ones.