In infectious disease, the reaction between the inciting microbe and host response produces inflammation. The same microbe, eg, Staphylococcus aureus, may produce markedly dissimilar clinical syndromes when present in individuals with different degrees of host responsivity. Immunoglobulins were quantitated in 54 patients with bacterial blepharoconjunctivitis who had been subclassified according to a severity gradient. Patients with severe staphylococcal disease demonstrated low serum IgM values, although the blepharoconjunctivitis group as a whole was within normal limits. The role of the antigen-antibody reaction in producing clinical disease and its therapeutic implication is discussed.