The oxygen consumption rate (QO2) of granulation tissue from cylinders implanted in bipedicle tube flaps of rabbits was measured weeks 2 to 7 in vitro in a Biological Oxygen Monitor. Granulation tissue from cylinders implanted in skin folds was used as control. The QO2 of granulation tissue decreased slowly as the oxygen tension in the medium fell. All measurements were made at an oxygen tension of 75 mmHg. At week 2 the QO2 of granulation tissue in flaps was high and a decrease occurred between week 2 and week 4. A further decrease took place between weeks 6 and 7 and a very low QO2 was found at week 7. Control granulation tissue showed a higher QO2 than skin flap granulation tissue at weeks 3, 4, 5 and 7.