Two commercially available kits were compared to an enzyme-linked immunosorbent assay (ELISA) for detection of Haemophilus influenzae type b antigen polyribophosphate in clinical specimens with infections proved by culture. Methods employed by the kits were latex agglutination (LA) and staphylococcal coagglutination (COA). The COA kit detects H. influenzae type b and types a and c-f with a polyvalent antiserum, whereas the ELISA assay and the LA kit detect only type b. A total of 139 specimens (41 spinal fluid, 35 urine, 25 serum, and 38 sputum) were tested. All spinal fluid samples positive by culture were positive by all three procedures. Of urine specimens from patients with a variety of H. influenzae type b infections, 13 of 15 were positive by ELISA, 8 of 15 by COA, and 8 of 14 by LA. Of serum samples collected from the same patients at various times during their illness, 8 of 15 were positive by ELISA, 6 of 15 by COA, and 10 of 15 by LA. Of sputum samples positive by culture for H. influenzae type b, 14 of 17 were positive by ELISA, 9 of 17 by COA, and 4 of 16 by LA. The ability to detect additional serotypes of H. influenzae was shown by the COA kit, which detected H. influenzae type a in spinal fluid from a patient with type a meningitis proved by culture.