Olfactory sensory neurons expose to the inhaled air chemosensory cilia which bind odorants and operate as transduction organelles. Odorant receptors in the ciliary membrane activate a transduction cascade which uses cAMP and Ca(2+) for sensory signaling in the ciliary lumen. Although the canonical transduction pathway is well established, molecular components for more complex aspects of sensory transduction, like adaptation, regulation, and termination of the receptor response have not been systematically identified. Moreover, open questions in olfactory physiology include how the cilia exchange solutes with the surrounding mucus, assemble their highly polarized set of proteins, and cope with noxious substances in the ambient air. A specific ciliary proteome would promote research efforts in all of these fields. We have improved a method to detach cilia from rat olfactory sensory neurons and have isolated a preparation specifically enriched in ciliary membrane proteins. Using LC-ESI-MS/MS analysis, we identified 377 proteins which constitute the olfactory cilia proteome. These proteins represent a comprehensive data set for olfactory research since more than 80% can be attributed to the characteristic functions of olfactory sensory neurons and their cilia: signal processing, protein targeting, neurogenesis, solute transport, and cytoprotection. Organellar proteomics thus yielded decisive information about the diverse physiological functions of a sensory organelle.