Detailed restriction maps of the plasmid SCP2* and its deletion derivative pSCP103 were constructed. DNA fragments carrying hygromycin (Hyg), thiostrepton (Thio) or viomycin-resistance (VioR) determinants were inserted into pSCP103, and various segments were deleted from the resulting plasmids. Changes in plasmid phenotypes associated with these insertions and deletions allowed the localisation and characterisation of plasmid replication, stability, transfer and fertility functions. Several useful cloning vectors were constructed. They are able to maintain large (greater than 30 kb) DNA inserts, with stable inheritance at a low copy number (1-2 per chromosome) and without structural rearrangements, in Streptomyces hosts. The vectors have a broad host range in the genus Streptomyces. One of them (pIJ903) is a shuttle vector for Streptomyces and Escherichia coli.