In the present study we have shown that quinolinic aromatic aminoxyls are very efficient in protecting lipids of endoplasmic reticulum membranes against hydroperoxide-induced oxidation. The efficacy of these aminoxyls as protectors of lipids was much higher than the water-soluble 4-OH-TEMPO. We have also shown that QAL causes distinct changes of the morphology of mitochondria: from filamentous to granular enlarged structure via the folding of the former. QAL induces also perinuclear clustering of mitochondria. C-QAL as well as 4-OH-TEMPO treated cells revealed filamentous and scattered pattern of mitochondria. Antioxidant activity of QAL as well as morphological changes of mitochondrial raise the possibility that this drug can affect cell physiology via changes of mitochondrial function.