The endocannabinoid anandamide alters mitochondria-dependent signal transduction, thus controlling key cellular events like energy homeostasis and induction of apoptosis. Here, the ability of anandamide to directly affect the integrity of mitochondria was investigated on isolated organelles. We found that anandamide dose-dependently increases mitochondrial swelling, and reduces cytochrome c release induced by calcium ions. The effects of anandamide were independent of its target receptors ( e. g., cannabinoid or vanilloid receptors), and were paralleled by decreased membrane potential and increased membrane fluidity. Overall, our data suggest that anandamide can impact mitochondrial physiology, by reducing calcium sensitivity and perturbing membrane properties of these organelles. (C) 2009 Elsevier Inc. All rights reserved.