Genetic studies of atopy-associated traits require unambiguous phenotypes to avoid both type 1 and 2 errors. The German Multicenter Allergy Study has provided a birth cohort with longitudinally well defined and stable phenotypes. We summarize data on candidate gene studies on chromosomes 12q, 5q, and 13q using high total IgE and atopic dermatitis (AD) as the most common atopy associated phenotypes in early childhood. We also present data on a functional RANTES promoter polymorphism that we recently identified. A significantly higher frequency of the mutant allele was seen in individuals of African descent compared to Caucasian subjects. In addition, an association of the polymorphism with AD could be demonstrated in the MAS cohort. Although the statistical approaches are limited, the MAS cohort has provided a valuable population for candidate gene studies in atopy.