Background: IgE-mediated sensitization is usually considered a dichotomous variable (either sensitized or not). Quantitative IgE antibody analysis may better predict the expression of wheeze. Objective: Within the context of a population-based birth cohort, we investigated the association among wheeze, lung function, and specific IgE antibody levels. Methods: Children (n = 521) were followed to age 5 years with repeated questionnaires, skin testing, and measurement of lung function (specific airway resistance) and specific serum IgE (ImmunoCAP). Results: Using specific IgE as a continuous variable, the risk of current wheeze increased significantly with increasing IgE to mite, cat, and dog (P <.0001). When IgE levels to these 3 allergens were summed, the probability of current wheeze increased 1.33-fold (95% CI, 1.21-1.47; P <.0001) per logarithmic unit increase, corresponding to an odds ratio of 3.1 at 10 and 4.25 at 30 kUA/L (kilo units of Allergen per liter). Similarly, increasing sum of mite-specific, cat-specific, and dog-specific IgE was associated with reduced lung function (P = .004). Among sensitized children (n = 184), the sum of mite, cat, and dog IgE was the strongest associate of current wheeze (odds ratio, 1.28; 95% CI, 1.13-1.46; P <.001), corresponding to an odds ratio of 2.56 at 10 and 3.32 at 30 kUA/L. There was no association between current wheeze and the size of skin test wheal. Furthermore, the sum of IgE to mite, cat, and dog at age 3 years increased the risk of persistent wheeze by age 5 years (2.15-fold/logarithmic unit increase in the specific IgE). Conclusion: IgE-mediated sensitization is not an all or nothing phenomenon. The probability of wheeze and reduced lung function increases with increasing specific IgE antibody levels. © 2005 American Academy of Allergy, Asthma and Immunology.