In order to facilitate the procedure of mammalian gene targeting, we have produced and functionally tested a series of generic vectors. Homologous recombination has been achieved with each vector. The vectors are designed for both replacement and insertional recombination, are suitable for 'hit and run' strategies and contain all necessary genetic elements for both positive-negative and promoterless/gene fusion enrichment of homologous integrations. Multiple unique restriction sites are included to simplify the incorporation of genomic targeting sequences.