Development of breathing behavior depends on the coordinated maturation of central and peripheral neural pathways, respiratory muscles, airways, and lung tissues. Each of these components contains cellular elements in which derangements of gene expression may perturb development of normal respiratory function. Application in recent years of genetic engineering techniques has led to detailed analyses of gene structure and function. In particular, targeted gene deletions provide the opportunity to relate gene function to physiologic mechanisms in intact animals. This review summarizes recent studies in mice designed to alter, by targeted disruption of specific genes, development of individual components of the respiratory control system. We also discuss an example of the human therapeutic potential of transgenic methods.