The early diagnosis and adequate treatment of respiratory complications in trauma cases has a decisive influence upon the patients' posttraumatic development. Pulse oximetry enables us to evaluate and monitor the prehospital respiratory situation objectively for the first time. Within a prospective study conducted from October 1988 to October 1989 in 336 unselected, primarily traumatized, emergency patients rescued by our "SAR Ulm 75" helicopter team, to determine the possibilities and limitations of this method, we maintained continuous pulse oximetric monitoring in all cases. The practical applicability and functional stability of the pulse oximeters used were adequate. On-the-spot intubation was necessary in 45% of the patients (or they were intubated prior to our taking over). Oxygen inhalation by nasal cannula was needed in 55%. While not being decisive for immediate intubation, monitoring with a pulse oximeter does play an essential role in controlling respiratory therapy. In 32% of our cases, pulse oximetric monitoring permitted early adjustment of the respiratory therapy to meet the patients requirements. This method is of special value in disclosing life-threatening respiratory complications (9.3%) i.e., valve pneumothorax. Within a group with a high percentage of multiple traumas (27%) and thorax traumas (39%), this was of enormous assistance in the differential diagnosis. Level and rate of increase of oxygen saturation can be an indication of the severity of a thorax trauma. The limitations of pulse oximetric monitoring, especially those resulting from low peripheral perfusion in trauma cases (7 patients), are fairly rare.