Several recent studies in adults have indicated that counterimmunoelectrophoresis (CIE) of sputum can distinguish persons with pneumococcal pneumonia vs those in whom merely colonization of pneumococcus occurs--CIE being positive in the former and negative in the latter. Counterimmunoelectrophoretic determinations were done on nasopharyngeal (NP) secretions in 20 children with bacterial pneumonia as evidenced by physical and radiological findings, leukocytosis, response to a penicillin, and in some cases, evidence of bloodstream invasion. Thirty-five children with other types of respiratory illness served as controls. Ten of 16 children from the pneumonia group had pneumococcal antigen in their NP secretions. Four of the six patients without pneumonia had evidence of disease associated with type 14 pneumococcus, which is not generally detected by CIE. The four additional patients with pneumonia had Haemophilus influenzae type b, and H influenzae type b antigen was present in the NP secretions. In the control group, one patient had pneumococcal antigen, and one patient had H influenzae type b antigen in the NP secretions, although 17/35 were positive for pneumococcus by culture. Counterimmunoelectrophoretic determinations of NP secretins are reliable in distinguishing patients with pneumococcal pneumonia vs those who are merely carriers (P less than .001).