Tumor necrosis factor alpha (TNF-alpha) levels were measured by immunoradiometric assay in chronically hemodialyzed patients consisting of 9 males and 3 females aged between 14 and 60 years. TNF-alpha levels were 5.47-15.1 pg/ml (mean 9.76 +/- 6.63) before hemodialysis (HD), and 5.75-58.55 pg/ml (mean 22.15 +/- 15.14) after HD. According to these results TNF-alpha levels in chronically hemodialyzed patients were within normal limits, but after 4 h of HD, higher levels of TNF-alpha were found.