Although patients with C3 complement deficiency rather than individuals with membrane attack complex (MAC, C5b-C9) deficiencies suffer from Hib infections, pointing to C3b opsonization as more important host defense against invasive Hib infection (23, 24), the relative importance of different host mechanisms for clearance of invasive Hib disease has not been studied side-by-side. The gene discussed is C5; the disease is complement deficiency.