Five immunological tests were evaluated for their ability to detect Streptococcus pneumoniae antigen in serum and urine simultaneously as a means of rapid diagnosis in 40 patients with bacteremic or non-bacteremic pneumococcal pneumonia or pneumonia with other etiologies. Serum and urine were screened in parallel with counterimmunoelectrophoresis (CIE), two commercial latex agglutination kits - the Slidex pneumokit (LA-SPK) and the Bactigen Streptococcus pneumoniae kit (LA-Bac) - the coagglutination Phadebact Pneumococcus test (CoA) and a newly developed enzyme-linked immunosorbent assay (ELISA) containing the immunoglobulin G fraction from rabbit pneumococcal antiserum. The detection rate for accumulated serum in bacteremic patients was 18% for LA-Bac, 24% for CIE, 47% for LA-SPK and CoA and 76% for ELISA, whereas antigenuria was present in only 29% for LA-SPK, 24% for CIE, 19% for CoA, 14% for LA-Bac and 5% for ELISA. Detection by ELISA of pneumococcal antigen in severely ill patients can predict bacteremia and rapidly confirm the diagnosis of pneumococcal pneumonia if sputum and results of blood cultures are not available.