Dr. Martinez and his group have found linkage between markers in chromosome 5q31 and both eosinophilia and a composite 'atopy' phenotype. The goal of the study is to identify the gene variants in 5q31-33 that are responsible for these two linkage signals. This will be done using the same population of families enrolled in the Tucson Children's Respiratory Study that have now been followed since the time of birth of the index child approximately 18 years ago. In the first specific aim, gene variants having a frequency of 2% or more in a group of 25 known genes in chromosome 5q will be identified. The 25 genes have been selected among those that have been mapped to the 28 cM interval that was tested for linkage in previous studies. The second specific aim is to perform linkage disequilibrium mapping using 100 known polymorphisms in the region of approximately 6.4 cM that shows the highest likelihood of containing the gene variants responsible for either or both of the eosinophilia and atopy linkage signals. Detailed local mapping using both published and newly discovered polymorphisms in and around the areas of positive signals will also be performed. Based on the previous experience of these investigators for the same chromosomal region, several association/linkage signals in chromosome 5q are expected to be found.