In light or dark grown Euglena gracilis cells, the DPG content, in contrast to the PG content, is dependent on the carbon source. These results are closely related to the electron microscopy observations, showing structural changes in mitochondria varying with the carbon source of the media.Two media have been used: the first one contains L-glutamic and DL-malic acid and the second contains DL-lactic acid. The phospholipidic analysis shows that PC and PE are the two main phospholipids.