Established expression vectors exploiting regulated promoters such as the lac or the promoters have economic and technical limitations when used for the industrial production of recombinant proteins. Consequently, alternative expression systems are being developed that can be more readily manipulated while maintaining high yields of protein. Several suitable expression vectors have been described for use in Escherichia coli that are based on promoters the activity of which is under metabolic control. This article discusses the advantages and disadvantages of a cross-section of these expression systems, how they compare with established systems and how they can be applied to the industrial-scale production of recombinant proteins.