Plasma concentrations of the cytokine tumor necrosis factor (TNF) were measured serially in 91 patients suspected of having septicemic melioidosis. This was confirmed in 55. TNF was detectable in admission plasma (TNF0) in 3 of 15 survivors of septicemic melioidosis and 21 of 26 fatal cases (P less than .001). The median (range) TNF0 concentration in melioidosis patients who died was 96 (1-4774) pg/ml, and the median time to death was 25 (5-672) h. TNF0 was inversely correlated with the lowest mean arterial pressure in the succeeding 12 h (Spearman's rank correlation coefficient = .67, 2P less than .001). Three patterns of TNF plasma concentrations were evident: relatively constant values between 100 and 500 pg/ml (n = 7), high admission concentrations (greater than 1000 pg/ml) associated with early death (n = 4), and an apparent pulse release after treatment, with peak values greater than 1000 pg/ml, which then declined with a mean (SD) apparent half-time of 131 (50) min (n = 8). Further studies are necessary to determine whether TNF contributes to lethality in melioidosis.