In this study the polymerase chain reaction was used to test for the presence of Chlamydia pneumoniae DNA in 118 middle-ear aspirates from 20 children with acute otitis media (AOM) and 53 children with otitis media with effusion (OME). C. pneumoniae was detected in 8 samples obtained from 5 children with OME and, together with Streptococcus pneumoniae, in a sample from 1 child with AOM. The mean age of these five children (6.6 +/- 1.4 years) was significantly higher than that of the 48 children with OME in whom C. pneumoniae could not be detected (4.3 +/- 1.9 years). The presence of C. pneumoniae in 9.4% of the examined children with OME suggests that C. pneumoniae might be a significant supplementary factor in the etiology of this common children's disease.