The triad of reversible airway obstruction, bronchial hyperresponsiveness, and airway inflammation characterizes asthma. The etiology of asthma is complex and involves the interaction of multiple genetic foci and a variety of environmental factors, such as protein allergens, chemical sensitizers, and viral or bacterial proteins. Candidate asthma genes have been identified that may be linked or associated with the asthmatic phenotype. Potential candidate asthma genes include cytokine genes, receptor genes, transcription factors, immune recognition genes, and genes regulating lipid mediator generation. Although polymorphisms within either the promoter or coding region of individual asthma candidate genes have been identified, the association between these genetic polymorphisms and the asthmatic phenotype remains incompletely defined. Furthermore, genetic polymorphisms mediating the asthmatic phenotype are rarely identified in individual patients. This manuscript reviews several of the specific mutations and polymorphisms that have been identified in candidate asthma genes, such as the high affinity IgE receptor, the &bgr;2-adrenergic receptor, the interleukin-4 promoter and receptor, the tumor necrosis factor gene, and the 5-lipoxygenase promoter.