The therapeutic use of iv immunoglobulins of the G class in association with antibiotics in patients with severe sepsis is reported. As compared to the randomized control group of patients treated with antibiotics alone, patient survival was only slightly improved (from 25% to 42%; NS); however, the defervescence time was significantly shorter (10 vs. 16 days), and a greater percentage of microbiologically positive cultures became negative (40% vs. 8%; p less than .01). The percentage of days on antibiotic treatment during ICU hospitalization was consequently reduced (38% vs. 95%; p less than .01). The therapeutic use of iv immunoglobulin G is discussed in terms of antibody substitution and modulation of the immune system.