Bacterial surface display in combination with fluorescence-activated cell sorting is a versatile and robust system and an interesting alternative approach to phage display for the generation of therapeutic affinity proteins. The system enables real-time monitoring and sorting of cell populations, which presents unique possibilities for drug development. It has been used to develop several affibody molecules currently being evaluated preclinically for the treatment and diagnosis of, for example, cancer and neurodegenerative diseases. Additionally, it can be implemented in other areas of drug design, such as for mapping epitopes and evolving enzyme specificities. Bacterial surface display in combination with fluorescence-activated cell sorting is a versatile and robust system for the generation of therapeutic affinity proteins. It has been used to develop affibody molecules for the treatment and diagnosis of, for example, cancer and neurodegenerative diseases.image