Our results show that, in all conditions tested, rRNA degradation is tightly connected with mitochondrial function and the active process of respiration. Rho0 cells that are less resistant to oxidative stress suffer severe rRNA degradation in the presence of H 2 O 2 , acetic acid and 60% glucose and during chronological ageing. Also, impediment of oxidative phosphorylation by protonpump inhibitors or by mutations in ATP/ADP carriers gives a similar outcome. In contrast, rRNA is markedly more stable when mitochondrial respiration is enhanced (e.g. by growth on glycerol versus glucose). This is consistent with the protective role of active mitochondria against the damaging effects of ROS on cellular components, rRNA destruction included. To begin with, several anti-oxidant enzymes localize to mitochondria and are more abundant in respiring cells. In addition, it has been proposed that some anti-oxidant activities may require energy (75) .