This study was carried out on 48 patients with ESRD undergoing hemodialysis treatment (29 males and 19 females, mean age 50.8 years) and renal transplantation (15 females and 33 males, mean age 42.2 years). The results were compared with a group of 44 healthy persons (23 females and 21 males, mean age 49.5 years). The aim of our investigation was to examine the content of fluoride in the mixed unstimulated saliva of the patients undergoing renal replacement therapy and in the control group of healthy persons. We studied the influence of hemodialysis on saliva fluoride levels. Saliva samples were collected by the spitting method according to Navazesh. Samples were collected before and after hemodialysis session and once in graft recipients and controls. Fluoride concentrations were determined with an Orion fluoroselective electrode model 96-09. The fluoride level in healthy persons was 4.92 +/- 2.30 micromol/L. Before hemodialysis, the mean fluoride level was 9.63 +/- 3.90 micromol/L and decreased significantly to 7.52 +/- 2.71 micromol/L after hemodialysis (p < 0.0001). Saliva content of fluorides in patients before and after hemodialysis was significantly higher than in healthy subjects and kidney graft recipients (p < 0.0001). There was no significant difference in fluoride concentration between patients after kidney transplantation and controls. The results suggest the need for individual fluoride supplementation in chronically hemodialysed patients.