The coding region for Olfr19, modified by introduction of the hemagglutinin epitope tag between the second and third exon, was linked to the 5' end of an IRES-tau-lacZ-loxP-tk-neo-loxP expression cassette. Insertion of this construct replaced the entire translated region of the endogenous gene, and placed expression of the inserted sequences under control of the endogenous regulatory sequences. Transient expression of Cre recombinase in C57BL/6 blastocysts excised the thymidine kinase and neomycin sequences. This allele expresses a bicistronic mRNA encoding Olfr19 and a bovine tau-beta-galactosidase fusion protein.