We examined and compared results from three assays, an enzyme-linked immunosorbent assay (ELISA) and two immune complex ELISAs for analysis of the serum antibody response to a native pneumococcal 37-kD common cell-wall protein by using acute- and convalescent-phase sera from 56 patients with community-acquired pneumonia. The sensitivities of the ELISA, the undissociated and dissociated immune complex assays were 85% (23 of 27), 78% (21 of 27) and 67% (18 of 27), respectively. To determine specificity, paired sera from patients with pneumonia of other bacterial etiologies were tested. The specificities were 83, 83 and 72% for the ELISA, undissociated immune complex, and dissociated immune complex, respectively. Based on this study, the sensitivities of the three assays were not statistically different. These tests could be used retrospectively to confirm invasive pneumococcal disease.