The clinical utility of the newly developed pressure swing adsorption (PSA)-type oxygen concentrator with a membrane humidifier that does not require added water for humidification was evaluated in 13 patients with chronic pulmonary disease who were receiving long-term oxygen therapy. PaO2 and the relative humidity were measured when the patient breathed air and oxygen from the new device via a nasal cannula. After using the new concentrator for 5 h, the patients were asked whether they experienced dry nasal passages or a dry throat. A significant difference between the PaO2 measured while the patients breathed room air and while they breathed oxygen from the new device was observed. A significant difference was observed between the relative humidity of room air (44.7 +/- 18.6%) and that of the oxygen flow (72.7 +/- 14.8%) from the new device. None of the patients experienced dry nasal passages, dry throat, or any other adverse effects. Since this new PSA-type oxygen concentrator with a membrane humidifier supplies well-humidified nasal oxygen without water, laborious cleaning of the container and changing of the water are not necessary, and may help to improve the patient's quality of life.