Oxpentifylline (pentoxifylline), which is known to have pharmacological effects in animal models of respiratory distress syndrome, multiorgan failure, and shock, was tested in human beings after injection of endotoxin. Of ten healthy volunteers, nine met the inclusion criterion of a rise in body temperature of at least 1.0 degrees C after 100 ng endotoxin (Salmonella abortus equi) as a bolus injection. Serum levels of tumour necrosis factor alpha (TNF) and interleukin-6 (IL-6) were both significantly higher than baseline levels 2 h and 3 h after endotoxin injection. 3 weeks later the nine volunteers were again injected with 100 ng endotoxin and oxpentifylline (500 mg over 4 h) was also infused. There was no rise in TNF levels, though IL-6 levels rose in parallel with body temperature. These data suggest that oxpentifylline blocks the endotoxin-induced synthesis of TNF in man and, therefore, could possibly have beneficial effects in clinical endotoxaemia.