Cytokines are essential mediators of immune response and inflammatory reactions. Patients with chronic renal failure (CRF) commonly present with abnormalities of immune function related with impaired kidney function and the accumulation of uremic toxins in addition to bioincompatibility of dialyzer membranes. During a hemodialysis (HD) session, cytokines are released mainly by monocytes activated by endotoxin-type compounds in dialyzer fluid, complement factors and direct contact with dialyzer membrane. The study included 15 CRF patients, aged 36.4 +/- 2.9 years, on regular HD maintenance therapy for mean 68 +/- 10 months and 15 healthy controls. It was designed to assess serum levels of a panel of inflammatory cytokines: IL-1beta, IL-2, IL-6, IL-8 and TNF-alpha in CRF patients on regular maintenance HD before, 20, 60 and 240 minutes of a single HD session in parallel with C-reactive protein (CRP) as an additional parameter. CRP concentration was increased in HD patients when compared with healthy controls. The concentrations of IL-1, IL-6, IL-8 and TNF-alpha were increased, whereas the serum level of IL-2 was not altered during a single HD session.