Background/Aims: Epidemiological, animal and human studies have indicated that selenium deficiency is a risk factor for death from malignant diseases. The mechanisms that could modify selenium status may, therefore, be of particular interest in hemodialysis patients, considering their high cancer mortality rates. We aimed at evaluating the effect of hemodialysis with polysulfone membranes on selenium status. Methods: Twenty- eight chronically dialyzed patients and 32 age-matched healthy controls were enrolled in the study. Serum and dialysis fluid selenium concentrations, serum total protein, and hemoglobin concentrations and serum glutathione peroxidase activity were determined before and after the hemodialysis procedure. Results: The (mean ± SD) serum selenium and total protein concentrations and glutathione peroxidase activities were significantly (p < 0.05) higher in healthy controls (75.9 ± 8.3 µg/l, 78 ± 6 g/l, and 23.8 ± 4.8 mU/20 µl, respectively) than in the patients. There was no significant difference between serum selenium concentration before (63.6 ± 11.6 µg/l) and after (64.4 ± 11.4 µg/l) hemodialysis sessions, although hemoglobin and total serum protein concentrations and serum glutathione peroxidase activities increased (from 98.5 ± 1.3 to 114.8 ± 1.5 g/l, from 64 ± 8 to 71 ± 9 g/l, and from 16.8 ± 1.8 to 18.9 ± 1.9 mU/20 µl, respectively) significantly (p < 0.05) during hemodialysis, indicating hemoconcentration. The selenium concentration doubled, and protein appeared in the dialysates during dialysis session. The correlation of the selenium concentrations with the protein concentrations in the dialysate is significant (p < 0.01) with a Spearman R value of 0.97. Conclusion: The results of the present study suggest that selenium is lost through the pores of polysulfone membranes during hemodialysis which is associated with their protein permeability.