Regular dialysis treatment (RDT) does not obviate hyperoxalemia of chronic renal failure (CRF). However, there is emerging evidence suggesting that current dialysis prescription is not always associated with progressive oxalate accumulation. In view of the controversy still concerning this issue we have investigated on plasma profiles and dialysis kinetics of oxalate in patients on RDT. Oxalate was determined by ion chromatography on serum ultrafiltrates and on the whole dialysate in 23 stable patients on RDT for end-stage renal failure unrelated to primary hyperoxaluria. Nine patients were on traditional hemodialysis (HD) and 14 on soft hemodiafiltration (HDF). Plasma profiles showed that dialysis patients were virtually always hyperoxalemic. Dialysis reduced plasma oxalate by more than 60%. There was a post-dialysis oxalate rebound averaging 9.6% at 30 minutes from the end of dialysis. Oxalate dialyzer clearances were mildly higher on HDF than on HD, and were lower than both urea and creatinine clearances, irrespective of the dialysis technique. Distribution space of oxalate was 21.5 1, that is 37.3% of dry body weight, and was quite similar to estimates obtained in normal subjects and in patients with CRF by alternative isotope dilution methods. Oxalate appearance rate averaged 337 +/- 69 mumol/24 h and was not different from the daily oxalate excretion assessed in 40 healthy subjects. Oxalate appearance was significantly related to urea generation and protein catabolic rates. From our results we conclude that, unless metabolic generation of oxalate is increased, current dialysis programs should prevent progressive oxalate accumulation in the majority of the patients.