The authors review the diagnostic protocol of mastoiditis based upon 382 cases with 1.3% errors (histological confirmation). Up to the present time, mastoidectomy was the only treatment which could be envisaged. In a new series of 90 cases, 48 constituted the control group and 42 the study group, trans-tympanic drains were inserted routinely in the latter. It was thus possible to avoid mastoidectomy in 62% of cases in the study group (evaluation based upon the number of ears). The period of postoperative observation was on average 8 months. No complications related to the drain were seen. Up to the present time, there exist no precise criteria which may be used to decide between insertion of a drain or mastoidectomy from the outset. Insertion of a drain must thus be considered as a therapeutic test, justified by its harmlessness and simplicity.