Abstract: The invention provides methods and compositions for evaluating modulators of the Stat6 signaling pathway; in a particular, transgenic mice comprising a transgene within a Stat6 allele locus, encoding a selectable marker and displacing the SH2-encoding domain of the Stat6 allele. More particularly, the transgene may comprise 3' and 5' regions with sufficient complementarity to the natural Stat6 allele at the locus to effect homologous recombination of the transgene with the Stat6 allele. Such mice provide useful animal models for determining the effect of candidate drugs on a host deficient in Stat6 function. The invention provides a variety of methods for making and using the subject compositions; in particular, methods for determining the effect of a candidate drug on a mouse deficient in Stat6 function and methods of evaluating the side effects of a Stat6 function inhibitor.