DNA and RNA fingerprinting based on arbitrarily primed PCR provides the most powerful tool for the study of genes. The basic techniques are described in detailed protocols including each step from template preparation to fingerprint visualization. Various protocols for the basic techniques allow to choose between alternative strategies. In addition to the general techniques specific research applications of particular interest are given such as gene mapping, detection of somatic mutations, gene abnormally expressed in tumors or differentially expressed genes by RNA fingerprinting.