We have used P element deletion derivatives at defined locations in the Drosophila genome to construct a 100-kb extended P element more than twice the size of any previously available. We demonstrate that this prototypical extended P element is capable of transposition to new sites in the genome. The structural and functional integrity of a transposed extended P element was confirmed using molecular, genetic, and cytogenetic criteria. This is the first method shown to be capable of producing large, unlinked transpositional duplications in Drosophila. The ability to produce functional transposable elements from half-elements is novel and has many potential applications for the functional analysis of complex genomes.