Although Peyton Rous showed that sarcomas could be induced in healthy chickens by injecting them with cellfree extract from the tumour of a sick chicken in 1911, 2 it was not until 55 years later that he won the Nobel prize for the discovery of transmission of Rous sarcoma virus, an oncogenic retrovirus. The link between viruses and human cancers was unknown in the 1960s, although Epstein-Barr virus (EBV) was identifi ed in 1964 in a cultured African Burkitt’s lymphoma cell line. 3 Studies of viral oncogenesis in the US neglected DNA viruses in favour of the newly discovered feline and bovine leukaemia retroviruses. In Dusseldorf, Harold zur Hausen induced chromosomal aberrations in mouse cells with a vaccinia virus. He later repeated the task, with more success, in Pennsylvania, with an adenovirus in cultured kidney lines. 4 There, he studied with Werner and Gertrude Henle, who had observed EBV in cultured Burkitt’s lymphoma cells using electron microscopy. Zur Hausen disputed the Henles’ view that a minority of lymphoma cells maintain a persistent infection before transmission. Instead, he postulated that EBV is present in all Burkitt’s lymphoma cells and might be spon taneously activated—a view infl uenced by observations that bacteriophages infect an entire culture and oc casionally produce lytic infection. Long before the invention of PCR, zur Hausen used hybridisation to identify EBV in the supposed “virus-free” Raji Burkitt’s lymphoma cell line. 5 Once the technique was established, zur Hausen found EBV nucleic acid (between 1–26 genome equivalents) in all the Kenyan Burkitt’s lymphoma and anaplastic nasopharyngeal carcinoma samples he studied, but none of the controls. 6