The targeted Stim2 gene encodes a protein involved in regulation of cytosolic and endoplasmic reticulum calcium levels and store-operated calcium channels. These Stim2fl mice possess loxP sites on either side of exon 3 of the targeted gene. Exon 3 encodes the C-terminal calcium-binding EF hand domain. Mice that are homozygous for this allele are viable and fertile. When these mutant mice are bred to mice that express Cre recombinase, resulting offspring will have exon 3 deleted in the cre-expressing tissues. Removal of the floxed sequence creates a null allele. When bred to a strain with Cre recombinase expression in T cells (see Stock No. 017336 for example), this mutant mouse strain may be useful in studies of development of regulatory T cells.