Chlamydia pneumoniae infection is often diagnosed by analyzing specific antibodies to C. pneumoniae in sera. The method which has been used as the reference method, or "gold standard", the microimmunofluorescence test (MIF), demands a high level of experience for proper interpretation. A number of commercial enzyme immunoassay (EIA) tests have been introduced to the market in the past few years. These provide objective reading of titers, but are genus specific and not species specific. The latest EIA introduced, LabSystems EIA for C. pneumoniae, was investigated using several groups of clinically relevant patient sera in a comparison with MIF. It was found that the LabSystems EIA did not discriminate between antibodies to C. trachomatis and C. pneumoniae when tested with sera containing high titers of C. trachomatis antibodies. The correlation between C. pneumoniae EIA and MIF IgG and IgA titers was, however, good in the patient groups not having a high background of C. trachomatis antibodies: hypertensives, n= 199 and patients with chronic C. pneumoniae infections and ischaemic heart disease, n=33. In conclusion, the LabSystems EIA is a method which can be useful for screening populations with low prevalences of C. trachomatis/C. psittaci infection for antibodies to C. pneumoniae. It cannot replace the MIF test due to the lack of discrimination between different chlamydial antibody types.