The influence of “Rhinotherrn ®” (humidified hot air ((43 °C)) insufflator for the nasal passages) on natal mucosa was evaluated functionally and morphologically. After 30 minutes, 2 hours and 4 hours insufflations to the nose, 40 mg of hoarseradish peroxidase (HRP, Sigma tipe vi: 0.5 mg per ml, in saline) was inhaled into the guinea pigs' nasal passage with a nebulizer. Then septal mucosa was removed and observed under a light microscope and an electron microscope (Hitachi H-600). The present study indicates neither permeability enhancement of the nasal mucosa nor the morphological changes of the cell membranes The organella showed no changes after “Rhinotherm ®” insufflation. Therefore, it can be concluded that “Rhinotherm ®” is not harmful to the nasal mucosa if it is used correctly.