Since continuous ambulatory peritoneal dialysis (CAPD) causes losses of certain plasma proteins and their ligands, we examined the serum concentrations of vitamin A and retinol-binding protein (RBP), as well as the concentrations of vitamin A in the skin and dialysis fluid from 32 patients on CAPD over a period of 1–30 months (mean 7.5). The mean values of vitamin A and RBP in serum were 2–4 times higher than those in the healthy controls; a consistent finding in patients with chronic renal failure. Similarly, the vitamin A concentrations in skin were elevated in the CAPD patients (p < 0.01). The vitamin A content of the dialysate (mean 1.4 μmol/24 h), which correlated significantly with the serum vitamin A concentration (r = 0.67), was constant during CAPD treatment. RBP was present in the dialysate and its concentration closely correlated with that of vitamin A (r = 0.95), indicating that the transperitoneal diffusion involved retinol-RBP. This conclusion was supported by calculations of clearance rates. Despite the considerable losses of vitamin A in CAPD fluid, the patients’ vitamin A concentrations in serum and skin remained elevated. Whether extended CAPD treatment ( > 30 months) may eventually affect the vitamin A situation in chronic renal failure warrants further observations.