To study the protein expression of endotoxin, interleukin 1beta (IL-1beta) and regulated upon activation, normal T expressed and secreted (RANTES) in effusions of secretory otitis media and their roles in the pathogenesis of secretory otitis media. Seventy-two effusion samples were taken from 53 patients with secretory otitis media by tympanocentesis. After swabs they were taken for bacteria culture. Limulus amebocyte lysate (LAL) test was used to quantify the content of endotoxin, radioimmunoassay to analyze the level of IL-1beta and enzyme-linked immunosorbent assay (ELISA) to detect the concentration of RANTES. Endotoxin, IL-1beta and RANTES were detectable in 80.9%, 77.8% and 70.8% of middle ear effusion, with mean levels of (35.2 +/- 51.6) EU/ml, (1.10 +/- 0.84) microg/L and (0.52 +/- 0.43) microg/L respectively. All of them showed higher concentration in the mucoid-type effusions than those in the serous-type effusions (P<0.05). Higher levels of the endotoxin and RANTES (P<0.05) were found in longer cou