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 to 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 dialyzate 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). Dialysis prescription was set so as to obtain similar KT/V of urea. Mean dialyzer clearance of oxalate (KdOx) was calculated by standard procedures and was compared to urea (KdUrea) and creatinine (KdCr) clearances. Oxalate removal was measured on the whole spent dialyzate. Distribution volume of oxalate (VOx) was estimated by assuming a single-pool model and was used to estimate the oxalate appearance rate (OxAR). Plasma profiles showed that dialysis patients were virtually always hyperoxalemic. However, the threshold of supersaturation for calcium oxalate was exceeded in only 13 of 138 (9.4%) assayed ultrafiltrates, 13% on HD and 7.1% on HDF. Dialysis reduced plasma oxalate by more than 60%. There was a postdialysis oxalate rebound averaging 9.6% at 30 min from the end of dialysis. Plasma oxalate predialysis was independent of sex, age and time on dialysis. KdOx was mildly higher on HDF than on HD, and was lower than both KdUrea and KdCr, irrespective of the dialysis technique.(ABSTRACT TRUNCATED AT 250 WORDS)