Gene ablation, also known as knockout, is a powerful method to analyze gene function in vivo. Many integrin genes have been disrupted already, confirming but also contradicting previous results (1). In addition, new functions have been revealed, significantly increasing our understanding of the biological roles of integrins. Knockout of the remaining integrins will similarly elucidate their function during development. In addition, knockins of subtle mutations (2,3) and conditional knockouts (4,5), resulting in tissue-specific or temporally restricted gene ablation, will allow us to assess structure-function relationships of integrins in vivo and to investigate the function of integrins in a specific cell type at a specific time point in development.