Plasma concentrations of soluble interleukin (IL)-1 receptor type II, IL-10, and IL-13 were measured in 42 patients with clinically defined sepsis during a 3-day follow-up and in 7 healthy humans after intravenous injection of endotoxin (2 ng/kg). Levels of soluble IL-1 receptor type II were persistently elevated in patients with sepsis than in healthy controls and higher in nonsurviving patients (n = 22) than in surviving patients (n = 20) at all time points. IL-10 was found in the circulation of 81% of patients with sepsis, while it was not detectable in normal plasma. During follow-up, IL-10 remained invariably high only in nonsurviving patients, while it significantly decreased in survivors. Endotoxin induced IL-10, while soluble IL-1 receptor type II remained unchanged. IL-13 remained undetectable in the vast majority of patients and was not induced by endotoxin. Enhanced IL-13 production does not seem to be part of an inducible host defense mechanism during sepsis.