A study was undertaken to determine the incidence of chlamydial respiratory infection in paediatric patients during a 12-month period by antigen detection. Nasopharyngeal aspirates (NPA) from 514 patients were screened for genus-specific chlamydia antigen using the Pharmacia Chlamydia enzyme immunoassay (EIA) and Kallestad immunofluorescence (IF) assays. EIA screen-positive samples were confirmed by specific blocking antibody. Specimens which were EIA positive or IF positive were cultured for chlamydia. The NPAs from 7 patients were positive in the EIA and IF assays. Four of these patients were culture positive for chlamydia. Our results showed that the incidence of chlamydia respiratory infection by antigen detection was 1.4% or 0.8% if confirmed by culture.