OBJECTIVE To examine whether probiotics would reduce the occurrence or duration of acute otitis media (AOM), or the nasopharyngeal carriage of otitis pathogens in otitis-prone children. METHODS During this double-blind, placebo-controlled, randomised, 24-week intervention, 309 otitis-prone children (10 months-6 years) consumed either one probiotic capsule (Lactobacillus rhamnosus GG and LC705, Bifidobacterium breve 99 and Propionibacterium freudenreichii JS) (n=155) or placebo (n=154) daily. Clinical examinations were carried out and nasopharyngeal samples taken three times. Parents recorded the symptoms of upper respiratory infection (URI) in a diary. RESULTS Probiotic treatment did not reduce the occurrence (probiotic vs. placebo: 72% vs. 65%, OR=1.48, 95% CI 0.87-2.52, p=n.s.) or the recurrence ( three) of AOM episodes (18% vs. 17%, OR=1.04, 95% CI 0.55-1.96, p=n.s.). The median duration of AOM episodes was 5.6 (IQR 3.5-9.4) vs. 6.0 (IQR 4.0-10.5) days, respectively (p= n.s.). There was a tendency showing a reduction in the occurrence of recurrent (4 to 6) respiratory infections in the probiotic group (OR for 4 URIs: 0.56, 95%CI 0.31-0.99, p=0.046; OR for 6 URIs: 0.59, 95% CI 0.34 to 1.03, p=n.s.). Probiotics did not affect the carriage of Streptococcus pneumoniae or Haemophilus influenzae, but increased the prevalence of Moraxella catarrhalis (OR=1.79, 95% CI 1.06-3.00, p=0.028). CONCLUSIONS Probiotics did not prevent the occurrence of AOM or the nasopharyngeal carriage of otitis pathogens in otitis-prone children. A tendency showing a reduction in recurrent respiratory infections must be confirmed in further studies.