The acceptability of viral vaccines manufactured in culture of continu
ous cell lines opened the way to a new technology of vaccine preparati
on. The large scale cultivation of continuous cell lines contributed g
reatly to the improvement of the safety and the consistency of viral v
accines. Experimental studies concerning residual cellular DNA and its
oncogenic potential showed clearly that this material is not able to
induce tumours. The small amounts of cellular DNA present in the final
product, and the deleterious effect of the vaccine manufacturing proc
ess on the integrity and biological activity of DNA, both contribute t
o regarding residual cellular DNA as an issue of no practical importan
ce. There is no evidence that limits on the concentration of residual
cellular DNA in the final product is scientifically justified. (C) 199
5 The International Association of Biological Standardization