To investigate the incidence of hypoxemia which was defined as arterial blood oxygen saturation (SaO2) of 90% or less following general endotracheal anesthesia, 112 adult patients were randomly allocated to one of 8 groups aceording to oxygen administration or not. SaO2 was continually measured during postanesthetic period using a pulse oximeter (Nellcor, N-100 C, USA). The incidence of hypoxemia was lower in oxygen administration groups (5%) than in no administration groups (14%) in the recovery room. The mean discharge time of oxygen administration groups in the recovery room (37.9 min) was significantly shorter than that of no administration groups (45.6 min) (P=0.003). There were two cases of hypoxemia during transfer of patients from the operating room to the recovery room. The incidence of hypoxemia in oxygen administration groups (9%) was lower than no oxygen administration groups (71%) during 5 minutes after endotracheal extubation. It was coneluded that the incidence of hypoxemia can be reduced by administrating oxygen during postanesthetic period. Therefore, it is recommended that oxygen should be administered to all postoperative patients for prevention of hypoxemia following general endotracheal anesthesia.