1. Unrestrained Xenopus with access to air had an oxygen consumption, as measured at 20 °C by manometric and electrode techniques, of approximately 4.5 ml O2 100 g-1 h-1 of which 1.1 ml was taken in through the skin.
2. Measurements of body volume showed that the rate of oxygen uptake from the lungs was high when the animal was at the surface but fell rapidly during the first few minutes of a dive.
3. Oxygen tensions in systemic (80 mmHg) and pulmocutaneous (60 mmHg) vessels provided evidence for separation of blood flows in the ventricle of the animal when breathing air. The tensions fell in all parts of the circulation throughout a dive.
4. The above data, together with a conventionally determined oxygen dissociation curve, show that both blood and lungs are used to a limited extent as oxygen stores during a dive, the blood being more important. The stores do not permit tissue consumption to go on at a uniform rate throughout a normal breathing-diving cycle.