Whether gene expression is useful in discriminating different atopic phenotypes is unclear. The aim of the study was to evaluate a gene-expression score for the diagnosis of atopy and asthma and to assess disease activity as a guide for therapeutic decisions. Purified mRNA from PBMCs of 18 atopic asthmatic subjects, 8 atopic nonasthmatic subjects, and 14 healthy control subjects was hybridized to cDNA membranes. A composite atopy gene expression (CAGE) score was determined by using 10 genes dysregulated in atopic individuals according to a specific algorithm. The CAGE score was better than total IgE in differentiating atopic from nonatopic subjects (sensitivity, 96%; specificity, 92%). Correlation between the CAGE score and total IgE (P <.001) was found, and there was a trend for correlation with asthma severity (P = .051). The CAGE score was able to quantify phenotype-specific alteration in gene expression of atopic individuals. The CAGE score might be used as a diagnostic tool or to monitor the effects and side effects of therapy.