Diagnosis of infection caused by Chlamydia pneumoniae, a newly recognized respiratory pathogen, has proved difficult. Between July 1987 and April 1988, culture and serologic tests for C. pneumoniae were done on specimens from 49 patients with pneumonia seen at an Atlanta hospital emergency room. Cultures from 3 patients (6%) grew C. pneumoniae. Genus-specific Chlamydia complement fixation titers and microimmunofluorescence titers for C. pneumoniae were suggestive of acute infection in all 3 culture-positive patients. Three other patients had evidence of acute disease by published criteria for antibody titers. Most studies of C. pneumonia have not had culture-proven cases; the 6% rate of positive cultures in this study support the role of C. pneumoniae as a cause of pneumonia. More widespread availability of simplified culture systems for C. pneumoniae is needed. Caution should be used when interpreting serologic tests in the absence of culture confirmation.