Olfactory receptor genes whose expression in the mouse olfactory epithelium was confirmed in this study. Genes whose expression has been confirmed by our cDNA screen are colored blue on a phylogenetic tree of 1,107 intact mouse olfactory receptors. Genes whose expression was confirmed by PCR methods are colored red (genes listed in Additional data file 1 were confirmed by specific PCR of the cDNA library or reverse-transcribed RNA, and genes confirmed using the class I degenerate primer for RT-PCR are AY317681, AY317698, AY317700, AY317767, AY317773, AY317774, AY317797 and AY317923). Other olfactory receptors are colored gray, and a chemokine outgroup is colored black. Class I olfactory receptors are bracketed, and the remaining olfactory receptors are class II.