TARGET (Trial of Alternative Regimens in Glue Ear Treatment) is a multicentre UK randomized controlled trial (RCT) comparing bilateral ventilation tubes with and without adjuvant adenoidectomy against non-surgical management in children with bilateral, persistent otitis media with effusion (OME). This paper compares the recruited and randomized children with those that, although eligible, were not included in the RCT for various reasons. This is necessary to identify any potential bias in the overall estimate of treatment effectiveness. At the first visit, 1315 children with OME satisfied the criteria of age (3 years 3 months-6 years 9 months), no previous ear or adenoid surgery, tympanometric evidence of fluid (bilateral B or B + C2) and a hearing loss (conductive loss in both ears of > or =20 dBHL). Of these children, 151 (11%) were not followed up because of overriding concern and 70 (5%) because of parental refusal. Of the 506 children eligible for randomization, because of persistence over 12 weeks of watchful waiting of bilateral OME with the same criteria, 20 (4%) were not randomized because of overriding concern and 75 (15%) because of parental refusal. The distribution of the potential effect modifiers was determined for each group. At the first visit, the only significant differences (P < 0.05), comparing those not recruited because of overriding concern with those recruited, were in respect of sex (61% girls compared with 52% boys) and hearing level (34.6 compared with 33.0 dBHL). At the second visit, the only significant difference involved less frequent upper respiratory tract infections (URTIs) in children whose parents refused to allow randomization (8% compared with 18% had had episodic URTI more often than once every 3 months). It is probable that the findings from the TARGET trial will translate to the entire clinic population in this age group as long as they meet the same audiometric and tympanometric criteria. The differences found can be handled by presentation of disaggregated results.