Emphasis on minimally invasive options for the surgical treatment of stress urinary incontinence (SUI) has resulted in the development of agents and techniques that improve these conditions substantially towards social continence, but currently give suboptimal cure/dry rates. The application of injectable therapy as an office procedure implies the potential for cost-efficient treatment for selected patients with UI. Continuous advances in materials technology have provided the possibility that many new urethral bulking agents will soon be available. Experience continues to accrue in clinical trials for urethral bulking with these agents, while parallel use for the indication of paediatric vesico-urethral reflux has also provided evidence of biological activity related to these compounds. The agents that are closest to complete analysis are synthetic and represent various material types and characteristics. As these materials develop, understanding of the preferred injection technique also is being gained. The delivery method and site might prove to substantially alter the biological activity of these compounds.