Insights into the complex genetic factors underlying asthma and atopy have arisen from investigating genes whose functions are likely to be involved in the pathogenesis of these disorders. Candidate genes have now been studied on 13 human autosomes, and genetic linkage analysis and association studies have identified potentially important genes on chromosomes 5, 6, 11 and 14. However, these four regions do not account for all the heritability of these disorders, and additional regions are now being identified by systematic searches of the whole genome.