Recent animal and human trials of bacteriophage therapy have demonstrated its potential to alleviate bacterial diseases, both in internal and in external applications. The regulatory requirements are becoming clearer as more examples are presented. A core of GLP (Good Laboratory Practice) studies will be needed to validate safety and clinical trials to validate efficacy. GMP (Good Manufacturing Practice) production requirements and quality issues will mean that comparable costs to the production of conventional antibiotics should be anticipated. The definition of the 'active substance' will be central to the success of bacteriophage therapy to ensure that the variety and evolutionary potential of bacteriophages are exploited.