The terms "adenoiditis" and "adenoid hyperplasia" are often used interchangeably to describe posterior nasal obstruction in children, tending to obscure indications for adenoidectomy. To more clearly define the role of the adenoid bed in nasal obstruction and its relationship to aural disease, we examined tissue obtained at adenoidectomy from 22 children via the quantitative bacteriological technique. In three patients, adenoidectomy was performed for nasal obstruction alone, in nine patients for serous otitis media and nasal obstruction, and in ten patients for nasal obstruction with serous otitis media and recurrent bacterial otitis. Using the criteria that 10(5) bacteria per gram of tissue indicates infection, 90% of the patients in the last group had infected adenoids vs 8% of the patients in the first two groups. Quantitative immunoglobulin levels, WBC counts, or preoperative antibiotic therapy was not helpful in determining which patients had infected adenoids. Pressure-equalizing tubes were placed when appropriate. A follow-up of nine to 22 months is included.