Transient elevations of intracellular Ca 2ϩ play an important role in regulating the sensitivity of olfactory transduction, but such elevations have not been demonstrated in the olfactory cilia, which are the site of primary odor transduction. To begin to understand Ca 2ϩ signaling in olfactory cilia, we used highresolution imaging techniques to study the Ca 2ϩ transients that occur in salamander olfactory receptor neurons (ORNs) as a result of cyclic nucleotide-gated (CNG) channel activation. To visualize ciliary Ca 2ϩ signals, we loaded ORNs with the Ca 2ϩ indicator dye Fluo-3 AM and measured fluorescence with a laser scanning confocal microscope. Application of the phosphodiesterase inhibitor IBMX increased fluorescence in the cilia and other neuronal compartments; the ciliary signal occurred first and was more transient. This signal could be abolished by lowering external Ca 2ϩ or by applying LY83583, a potent blocker of CNG channels, indicating that Ca 2ϩ entry through CNG channels was the primary source of fluorescence increases. Direct activation of CNG channels with low levels of 8-Br-cGMP (1 M) led to tonic Ca 2ϩ signals that were restricted locally to the cilia and the dendritic knob. Elevated external K ϩ , which depolarizes cell membranes, increased fluorescence signals in the cell body and dendrite but failed to increase ciliary Ca 2ϩ fluorescence. The results demonstrate the existence and spatiotemporal properties of Ca 2ϩ transients in individual olfactory cilia and implicate CNG channels as a major pathway for Ca 2ϩ entry into ORN cilia during odor transduction.