To visualize odor detection in individual cilia of olfactory sensory neurons we have developed a new approach by using high-resolution calcium imaging techniques. Laser scanning confocal microscopy revealed, for the first time, that odor stimuli induce transient Ca2+ elevations in single olfactory cilia. Pharmacological analysis indicates that these Ca2+ signals depend entirely on Ca2+ entry through activated cyclic nucleotide-gated (CNG) channels. This novel approach enables us to monitor the initial steps leading to olfactory perception in a spatially and temporally resolved manner.