The present study was carried out for the purpose of measuring platelet activating factor (PAF) and leukotrienes (LTs) in middle ear fluid (MEF) or in otorrhea of children with acute otitis media (AOM), with secretory otitis media (SOM), and with chronic otitis media (COM) on the acute exacerbation. PAF, LTC4, and LTD4+LTE4 concentrations were measured by radioimmunoassay in purulent MEFs obtained from 15 ears of 15 children with AOM, in mucoid or gluey MEFs from 16 ears of 15 children with SOM, and in purulent otorrhea from 9 ears of 9 children with COM on the acute exacerbation. PAF concentrations were 25.4 +/- 9.0 ng/mg total phospholipid (TPL) in AOM, 4.9 +/- 1.9 ng/mg TPL in SOM, 20.7 +/- 15.7 ng/mg TPL in COM, demonstrating significant differences between AOM and SOM (p < 0.05) and between COM and SOM (p < 0.01). LTC4 concentrations were 92.9 +/- 73.8 pg/mg total protein (TP) in AOM, 52.0 +/- 42.5 pg/mg TP in SOM, and 28.5 +/- 11.2 pg/mg TP in COM. LTD4+LTE4 concentrations were 326.5 +/- 177.0 pg/mg TP in AOM, 288.2 +/- 144.6 pg/mg TP in SOM, and 94.0 +/- 58.1 pg/mg TP in COM, demonstrating significant differences between AOM and COM and between SOM and COM (p < 0.01). The results obtained indicated that PAF was involved in the onset of AOM and COM on the acute exacerbation, and that LTs played an important role in SOM.