- OBJECTIVES—To study the concentration of interleukin 8 (IL-8) in the middle ear fluid of children with acute otitis media and the association between IL-8 concentrations, aetiology of acute otitis media, and bacteriological sterilisation. STUDY DESIGN—Middle ear fluid was obtained by tympanocentesis at enrolment (day 1) and on day 4-5 in 81 children aged 3-36 months with acute otitis media who received antibiotic treatment. IL-8 concentrations were measured by enzyme linked immunosorbent assay. RESULTS—101 samples were obtained on day 1 and 47 samples on day 4-5. 94 pathogens were isolated in 79 of 101 samples obtained on day 1: 56 Haemophilus influenzae, 35 Streptococcus pneumoniae, 2 Moraxella catarrhalis, and 1 Streptococcus pyogenes. Among 40paired, initially culture positive samples, sterilisation was achieved on day 4-5 in 22 but not in 18 (13 H influenzae, 2 S pneumoniae, and 3 H influenzae and S pneumoniae concomitantly). IL-8 was detected in 96 of 101 and 46 of 47 samples obtained on days 1 and 4-5, respectively. Mean (SD) IL-8 concentration on day 1 was significantly higher in culture positive than in negative samples (12 636 (23 317) v 5920 (7080) pg/ml). In paired samples, IL-8 concentration fell in 12 of 22 ears in which sterilisation was achieved and in 9 of 21 ears with persistent or new infection. Mean (SD) IL-8 concentrations on day 4-5 were significantly higher in culture positive than in negative samples (15 420 (15 418) v 6695 (5092) pg/ml). CONCLUSIONS—Higher IL-8 concentrations are found in culture positive middle ear fluid in acute otitis media. Bacterial eradication is associated with a fall in these concentrations.