BACKGROUND: OBJECTIVE: METHODS: RESULTS: When compared with patients with PHG, patients with HIgM syndrome were found to have a significantly lower risk of nontypeable Haemophilus influenzae carriage in particular (relative risk, 0.39; 95% CI, 0.21-0.63). Moreover, patients with HIgM syndrome (including those unable to generate somatic hypermutations of immunoglobulin genes) displayed anti–nontypeable H influenzae IgM antibodies in their serum and saliva. Also, patients with HIgM syndrome had a lower incidence of acute respiratory tract infections. CONCLUSIONS: