We have characterized the organization and expression of odorant receptor genes clustered within approximately 100 kb of the zebrafish genome. Physical analysis of this genomic region reveals that the receptor genes are tightly linked in tandem arrays. The expression patterns of these genes were evaluated during development as well as in the adult olfactory epithelium. Highly related genes from this array are expressed individually in different olfactory neurons, suggesting that the discriminatory capacity of the vertebrate olfactory system has been maximized by segregating the most similar receptors into distinct cellular pathways. Furthermore, genes from this cluster are activated at different times of development. Together, these results indicate that genomically linked odorant receptor genes are not coordinately regulated.