Fifty patients (23 males and 27 females), with chronically hypertrophied and infected adenoids were subjected to adenoidectomy. Pre- and post-operative nasopharyngeal swabs were taken to study bacterial colonization of the nasopharynx both quantitatively and qualitatively. Twenty healthy controls were included in this study. The swabs were cultured on MacConkey's and Columbia blood agar plates. The rate of isolation of potentially pathogenic microorganisms decreased markedly following operation, while normal inhabitant organisms showed notable increase in their numbers post-operatively to reach a near normal level. It is concluded from this work that adenoidectomy produces a physiological effect on the nasopharyngeal microflora by conversion of an abnormal flora to a nearly normal one.