The odorant 2-isobutyl-3-methoxypyrazine binds to cow olfactory mucosa homogenate. The complex, which can be separated by gel filtration on Sephadex G-100, appears to be made up of four macromolecular species. No significant binding has been measured with respiratory epithelium. The binding disappears after treatment with proteolytic enzymes, or in a SDS containing buffer, thus indicating that the receptors are proteins. Complete loss of binding capacity has been also observed as a consequence of dialysis: this suggests the involvement of a low molecular weight component.