We recently identified a novel human sialic acid binding immunoglobulin-like lectin, Siglec-8, using mRNA from human eosinophils. To search for a mouse Siglec (mSiglec) ortholog of Siglec-8 and other mouse Siglec paralogs, we conducted public database searches with cDNA sequences of human Siglec-5 to -10 and identified two novel mSiglecs. One has significant sequence identity to human Siglec-5 and is a splice variant of mSiglec-F. The other has greatest sequence identity to human Siglec-10 (mSiglec-G). Both mSiglecs have extracellular Ig-like domains and intracellular tyrosine-based motifs. To determine whether these mSiglecs were relevant to mouse eosinophils, RT-PCR and Northern blot analysis were performed. We detected expression of mSiglec-5 (or -F), -10, and -E mRNA in purified mouse eosinophils, but Northern blot data comparing expression in tissues from normal, IL-5 transgenic, and allergen-sensitized and -challenged mice suggest that mSiglec-10 is probably most relevant to mouse eosinophils.