Both organ culture (chorioallantoic membrane) of striped muscle from mouse diapharagm and freeze-drying of myocardial cells presented very characteristic structures in mitochondria. The organ culture evidence ‘rod-like structures’ in the intracristal spaces of the cristae mitochondriales. It is believed that these structures are the central apparatus responsible for mitochondrial division. On the other hand, the freeze-dried mitochondria presented neither intracristal spaces nor a space in the outer mitochondrial membrane. Because these spaces appeared only after fixation and dehydration, it is discussed if they are really artifacts. The mitochondrial cristae appearing as united structures after the freeze-drying process have been compared to the rod-like structures appearing intracristally after organ culture and conventional preparation techniq