This study investigated the utility of an immunochromatographic test (ICT) for the detection of Streptococcus pneumoniae antigens in pleural fluid. Antigen was detected in 15 of 19 (79%) patients with pneumococcal pneumonia. The ICT was always negative in patients with non-pneumococcal pneumonia, but was positive in three cases with a non-infectious aetiology. In patients with pneumonia for which no pathogen was identified, antigen was detected in one of 24 pleural fluids tested. The ICT can be a valuable tool for the management of pneumonia because it can detect pneumococcal antigen in pleural effusion samples.