DNA fingerprinting by arbitrarily primed polymerase chain reaction (AP-PCR) is a simple and informative method to investigate genetic changes in cancers. The discovery of a mutator phenotype in hereditary non-polypotic colon cancer by the AP-PCR fingerprinting demonstrated the usefulness of this unbiased method. Due to its semiquantitative amplification of the target DNA, the AP-PCR fingerprinting can be applied to analyze numerical changes of chromosome fragments. A recent breakthrough of the chromosomal assignment of human AP-PCR products enabled us to do PCR-mediated molecular karyotyping of cancers. Application of single-strand conformation polymorphism (SSCP) analysis to AP-PCR products seems to be promising to elucidate somatic point mutations and hidden losses of heterozygosity in the anonymous regions in cancers.