Endotoxin is a potent activator of the complement system and other host immunoregulators, including the cytokines, tumor necrosis factor alpha, interleukin-1 beta, and interleukin-6. In this study, the potency of an endotoxin from bicarbonate dialysate was compared with endotoxins from two enteric microorganisms, Shigella flexneri and Escherichia coli. Endotoxin concentrations were standardized for the three endotoxins by use of the Limulus amebocyte lysate turbidimetric assay. Endotoxin potency was assessed by the comparative plasma concentrations of tumor necrosis factor alpha, interleukin-1 beta, and interleukin-6 after an in vitro whole-blood challenge by each type of endotoxin. Blood collected from 10 hemodialysis patients was spiked with 0.1, 1, and 10 ng/mL of E. coli and Shigella endotoxin and with 1 and 10 ng/mL of bicarbonate dialysate endotoxin. After incubation, plasma was separated and frozen at -70 degrees C until assayed for cytokine concentrations. Dialysate endotoxin was found to be 10 to 100 times less potent than E. coli and Shigella endotoxins. It was concluded that there are significant differences in the potency of endotoxins from different strains of bacteria and that these differences should be noted when designing or evaluating studies on the clinical effects of endotoxins in hemodialysis settings.