PCR can be used at different levels in oncology as many examples illustrate. Interchromosomal translocations that can be detected by PCR are very specifically found i.e. in follicular lymphomas. In the context of follow-up controls this may reduce recurrencies. By the identification of genetic lesions of an oncogene, aggressivity of a tumor may be estimated. PCR allows rapid analysis of such lesions. Analysing deletions of tumor suppressor-genes gains increasing importance in oncology. By amplification of microsatellites, presence of such a deletion may be detected. This analysis is not only important for studies of sporadic tumors but may also indicate in individual cases if the patient carries a predisposition for a certain tumor