4 different methods of nasal oxygen insufflation were studied in healthy adults and patients with broncho-pulmonary diseases: (1) O2-delivery by short double nasal catheter; (2) O2-delivery by short single nasal catheter; (3) O2-delivery by long nasopharyngeal catheter; (4) O2-delivery by short nasal catheter with compress (method of Poulsen). Results. In healthy adults and in hypoxemic patients the methods 3 and 4 yielded significantly higher values of arterial pO2 (application of 2 and 41 O2/min than the methods 1 and 2. Method 4, however, showed optimal oxygen delivery in combination with optimal humidification and warming of gas and should be prefe-red. A paradoxical fall of arterial pO2 during nasal oxygen administration is caused by augmented tidal and minute volume. This phenomena is demonstrated and discussed.