[New aspects of tumor genesis (author's transl)].

The author reports on the molecular biological site of action for cancerogenic substances. He shows how UV-radiation may lead to malignomas of the skin in the hereditary disease xeroderma pigmentosum and how ionising rays may cause changes of the DNA, the place of the genetic information. Since the virus genesis of malignant diseases has become more important lately, the author tries to point out the molecular biological connections of an eventual involvement of virus in the development of malignant diseases.