Three single nucleotide polymorphisms (SNPs) have been identified in Africans that are associated with increases in systemic NO production. These studies determine whether the NOS2 promoter SNPs are associated with differences in basal exhaled NO levels. The study of exhaled NO levels in individuals with asthma is confounded by the presence of cell types besides bronchial epithelium that produce NO, by differences in the severity of asthma and by the use of medications such as corticosteroids which alter exhaled NO levels.