Serum immunoglobulin E (IgE) is a quantitative trait associated with asthma. A variance components approach to the analysis of data from a subset of a founder population of Hutterites indicated that over half the variability in IgE levels may be due to genes. Two variance components methods suggest that the genetic model underlying IgE does not consist of a single major gene, but of multiple loci with more modest effects. Both approaches identified putative quantitative trait loci on chromosomes 1 and 21.