There are no reliable data on the volume of the drug reaching the affected tympanic cavity during the catheterization of Eustachian tube (ET). Objective: to conduct an experiment and to study the effectiveness of administering a drug into the tympanic cavity of the middle ear using an original ear catheter, which allows catheterization of ET in the direction of its lumen. The study included patients with unilateral OME (n=21, the duration of the disease from 2 to 3 months), who were recommended for the ventilation tube insertion. The main inclusion criterion was 3 degree of patency of the ET. The experiment was performed under endotracheal anesthesia. ET was catheterized before insertion of the ventilation tube, with a 0.9% saline in a volume of 7 ml, which was previously tinted with Brilliant Green. A syringe with a contrast solution was connected to an ear catheter and the drug was injected into the middle ear by the air-liquid substitution method. Otoscopically evaluated the following parameters: the volume of the injected drug (in ml) for the initial (V₁), partial (V₂) and complete filling of the tympanic cavity (V₃). As a result, it was found that 18 patients (85.7%) achieved full or partial filling of the tympanic cavity with a stained preparation: V₁=2.25 ml, V₂=7.0 ml in 11 (52.4%) patients, V₃=4.29 ml — in 7 (33.3%) patients. In this case, the minimum loss of the liquid form of the drug during CT catheterization is 1:2. In 3 (14.3%) patients there were no endoscopic signs of contrasting of the tympanic cavity.