The intensity of reaction in the IDEIA CHLAMYDIA test kit to lipopolysaccharide of seven strains of Chlamydia pneumoniae was examined by using highly purified elementary bodies (EBs). The strains were divided into two groups according to whether the EBs were pear-shape or round. The group with the pear-shaped EBs consisted of TW-183, AR-39 and AR-388 strains; the group with the round EBs consisted of IOL-207, Kajaani-6, YK-41 and KKpn-1 strains. The number of EBs at the cutoff level of the test kit were determined as follows: TW-183, 7.0 x 10(3); AR-388, 8.4 x 10(3); AR-39, 2.4 x 10(4); IOL-207, 6.0 x 10(3); Kajaani-6, 1.2 x 10(4); KKpn-1 2.8 x 10(4); and YK-41, 4.0 x 10(4) per assay. The number of EBs of C. trachomatis L2/434/Bu and C. psittaci Cal 10 were 1.0 x 10(3) and 2.7 x 10(4) per assay, respectively. The results demonstrated that the EBs of C. pneumoniae were detected with the test kit at different reaction intensities ranging from 6.0 x 10(3) to 4.0 x 10(4) per assay and that there was no correlation between EB number and morphology.