Genetic instability is very common amongStreptomyces strains and the affected strains display several distinctive phenotypes. In several cases DNA rearrangements, specifically deletions and amplifications of specific segments of DNA, were demonstrated. Depending upon the reproducible amplification of a segment in independent isolates one could predict the basic structural elements involved in the amplification process. In the case ofS. lividans 66,5.7 kb amplifiable DNA sequence is located near the end of the linear chromosome. Amplification of this sequence and deletion of the chromosome linked to it leads to the creation of a new end or in some cases even circularisation of the chromosome occurs. A model incorporating these aspects is discussed. The possible involvement of proteins encoded by the amplifiable region is also discussed.