Viral vaccines have been shown to contain residual host cell-DNA. There is no doubt about uptake and expression of foreign DNA in mammalian cells but the mechanism of transfection is not completely understood. It is suggested that DNA associates with several compounds and is transferred into the cell by endocytosis. In this study we estimate the potential of transfection of several original adjuvants by adding reporter plasmid DNA (pDNA) to vaccines. We used fibrosarcoma cells as an in vitro model and the results indicate that the cells are not able to express pDNA. Therefore we propose that adjuvants included in viral vaccines have no potential to transfect fibroblasts.