We evaluated the prevention of recurrences of acute otitis media (AOM) by bacterial polysaccharide immune globulin (BPIG), a hyperimmune human immune globulin prepared by immunizing donors with bacterial polysaccharide vaccines. We used a randomized, stratified, double-blind, placebo-controlled design. Children < or = 24 months of age with 1 to 3 prior episodes of AOM received BPIG, 0.5 ml/kg, or saline placebo intramuscularly at entry and 30 days later. During the 120-day follow-up period, AOM was diagnosed by using clinical criteria and was confirmed with tympanocentesis and culture of the middle ear exudates. Eighty-eight episodes of AOM were observed in 76 patients who completed the study. The incidence of AOM during the entire 120-day study period was similar in BPIG and placebo recipients. Pneumococcal AOM was significantly less frequent in BPIG recipients (0.21 episode per patient) than in placebo recipients (0.45 episode per patient; p = 0.05). Time spent free of AOM was significantly prolonged in recipients of BPIG, in comparison with placebo recipients (51 vs 35 days; p = 0.034). This study demonstrated that circulating antibody, even without stimulation of specific local immunity, may prevent infection of the middle ear. The use of immune globulin preparations for longer periods or at a higher dosage might decrease the incidence of recurrent AOM in otitis-prone children, and deserves further evaluation.