The genetics of atopy and asthma has become a very interesting area for research. Potential candidate genes identified either by the immunopathogenesis of asthma or bronchial hyperresponsiveness, or uncovered by the whole-genome screen, will lead to new and better ways of diagnosing asthma and, more importantly, the potential for drug discovery related to the products of the candidate genes identified in the various genome screening efforts. The candidate gene approach has been applied to the promoter region of a number of cytokine genes, both within and outside of the human 5q33 cytokine gene cluster. As a prototype for both cytokines, work relating to an interleukin (IL)-4 promoter polymorphism and an IL-10 promoter polymorphism will be reviewed as providing a potential molecular mechanism for dysregulation of these cytokine genes in asthma.