Objective: an in vitro study was conducted to set the necessary pressure in fluids that could break resistance and cross the opening of a tympanostomy tube. Methods: a water column model was created and graduated in centimeters from base to top. We adapted three sorts of tympanostomy tubes. In each model, fluids were tested (tap water, seawater, river water, soapy water and eardrops). The column was filled with fluid until a threshold was reached, flowing through the tube opening. The threshold

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... was registered and represented the pressure in cmH 2 O. Results: the results show that pressure is necessary so that a fluid can cross the opening of a tympanostomy tube. Conclusion: in spite of limitations of our in vitro study, the literature suggests that no ear protection is needed during shower, since there is neither direct flow of water nor pressure in the ear. Bathing with soapy water is potentially dangerous due to the reduction in surface tension. The direct relation of pressure and surface tension through the opening of tympanostomy tubes indicates the need to decrease pressure when diving and to avoid strong head movements in the water. J Pediatr (Rio J) 2002;78(6):475-80: water, ventilation tubes, otorrhea.