DQAsomes are mitochondriotropic cationic vesicles, which have been developed by us for the supposed transport of DNA to mitochondria in living cells [Pharm. Res. 15 (1998) 334]. Our strategy for the delivery of DNA into the matrix of mitochondria is based upon the putative transport of a DNA-signal peptide conjugate to mitochondria, the liberation of this conjugate from DQAsomes at the mitochondrial membrane followed by DNA uptake via the mitochondrial protein import machinery. As a first and important step towards delivery of DNA into mitochondria of living cells, we studied the DNA release from DQAsomes upon contact with non-energized mitochondria in vitro. Mitochondria were isolated from mouse liver and characterized by electron microscopy and the determination of mitochondrial marker enzyme activity. DQAsomes were added to DNA in the presence of SYBR Green I resulting in the formation of DQAsome/DNA complex and the complete loss of fluorescence. Following the addition of isolated mitochondria to DQAsome/DNA complex, the fluorescence signal was recovered due to the dissociation of DNA from its cationic carrier. Thus, DQAsome/DNA complexes were shown to release DNA upon contact with the surface of mitochondria thereby meeting a key requirement for our strategy towards mitochondrial DNA delivery.