Meignier et al. (1986) report the results of exposure of C57BL/6NCr mice to vaginal plugs containing live or inactivated herpes simplex virus 1 or 2 (HSV‐1 or HSV‐2) or recombinant viruses 5 times a week for up to 114 weeks. Genital organs showing abnormalities were transplanted into nude mice. Of 33 transplants, 13 produced subcutaneous tumors in nude mice and 12 were subsequently transplanted into C57BL/6NCr mice. We report that the DNA extracted from coded tumor tissues of nude mice and from normal viscera of the same rodents did not hybridize with HSV‐1 and HSV‐2 DNA probes representing the viral genomic regions shown previously to be capable of morphologically transforming cells in culture. The sensitivity of the assays was such that we could detect 0.5 copies of the HSV sequences of complexity equal to or greater than 1 Kbp per cell DNA equivalent. To control for the sensitivity of the assays in the actual hybridizations, the tumor‐cell DNA was also hybridized with a β‐globin mouse DNA probe. A striking feature of these control hybridizations was the detection of β‐globin polymorphism in some nude mouse tumors. The β‐ globin polymorphism allowed us to conclude that the analyzed tissues contained significant amounts of the tumor cells occurring in the C57BL/6NCr mice.