1. 1.

    Pre- and post-dive breathing patterns, blood oxygenation and acid-base balance have been examined in voluntarily and forcibly submerged Xenopus laevis.

  2. 2.

    Enforced 30-min dives led to a large acidosis with both respiratory (CO2) and metabolic (lactic acid) components. Complete recovery of the arterial blood variables after such dives took more than 4h.

  3. 3.

    Lung ventilation (measured by a pneumotachograph) following enforced dives was always markedly elevated compared with levels either before or after voluntary dives of the same duration.

  4. 4.

    In undisturbed Xenopus, diving freely for periods of 30 min or more, there was no accumulation of lactic acid and the fall in blood oxygen, increase in CO2 and the associated respiratory acidosis were all corrected within the first few breaths upon surfacing.

  5. 5.

    The evidence presented here leads us to conclude that anaerobiosis is unimportant during voluntary dives, even when these are of considerable duration.

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