This study compared oxygen tension (pO2) and percent oxygen saturation (SO2) in antecubital venous blood of six untrained (UT) and six endurance trained (ET) males during and following a graded leg exercise test to exhaustion on a cycle ergometer. Mean (+/- SE) resting values for pO2 were 29.3 (+/- 2.3) and 30.3 (+/- 2.0) mmHg, and SO2 were 51.8 (+/- 5.2) and 54.9 (+/- 4.6)% for the ET and UT men, respectively. At exhaustion pO2 decreased to 23.0 (+/- 4.5) and 23.3 (+/- 4.7) mmHg, while SO2 decreased to 29.6 (+/- 9.7) and 31.3 (+/- 9.7)% for the ET and UT subjects, respectively. There were no significant differences between the two groups in either pO2 or SO2 at rest or during exercise. However, there were marked increases in pO2 and SO2 during the 5 min recovery period for both groups. The ET cyclists demonstrated significantly higher pO2 and SO2 levels than the UT group at each min of recovery; e.g., at 4 min postexercise pO2 was 72 and 49 mmHg for the ET and UT men, respectively (p less than 0.05). The general rise in pO2 and SO2 for both groups was attributed to an increased arterialization of the antecubital venous blood while postexercise hyperventilation may have also elevated pO2 values. The higher values for the ET subjects during recovery were explained by a lower peripheral sympathetic tone and a presumably greater cardiac output at exhaustion for the ET group than the UT group, which may have allowed a relatively greater distribution of arterialized blood to the periphery.(ABSTRACT TRUNCATED AT 250 WORDS)