The main objective of the present study was to investigate associations between 121 Single Nucleotide Polymorphisms (SNPs) of NOS1, NOS2 and NOS3 genes with 1) the three biological phenotypes of the nitrate-nitrite-NO pathway [3]: FeNO levels, total nitrite-nitrate levels measured both in plasma and in exhaled breath condensate, and 2) blood eosinophil counts, in 1277 asthmatic and non-asthmatic adults from the French Epidemiological study on the Genetics and Environment of Asthma (EGEA). Here, NOS2 is linked to asthma.