During the growth of multiple-shoot cultures of Ruta graveolens, oxygen and carbon dioxide exchanges were continuously and simultaneously measured. The shoots subcultured on a medium containing 166 mM glucose showed a marked respiration rate. Even under light, CO2 concentrations reached 4000 to 6000 cm3 m-3. Photosynthesis never compensated for respiration. These cultures were photomixotrophic. A change of respiration and photosynthesis occurred between the 30th and the 32nd day of culture, with a high respiration rate. When the shoots were subcultured on a medium containing 41 mM glucose, it was possible to obtain photoautotrophy after two weeks under high irradiance (150 umol m-2 s-2), and after three weeks under low irradiance (60 μmol m-2 s-1), the CO2 concentrations being 1100 and 600 cm3 m-3 respectively.