A series of experiments was conducted to study the base composition of DNA in AVl2-induced tumor and host cells by paper chromatography, and it was found that DNA per cent. guanine-cystosine contents were around 42 % in both of them. The base composition of DNA of AV12 itself differs considerably from that of AVl2-induced tumor cells, while
the DNA of tumor cells shows the property similar to that of host cell DNA. The genetical relationship among virus, host cells and tumor cells was discussed.</p