The laminar segregation of sensory neurons expressing a distinct receptor type was determined in tissue sections through the olfactory epithelium by in situ hybridization employing receptor-specific probes. Reactive cells were restricted to the mid-zone of the epithelium, the location of mature neurons. Detailed analyses revealed that neurons expressing a distinct receptor type were distributed in a characteristic manner throughout the layers of the neuronal zone, i.e. they were preferentially located in a particular laminar zone of the epithelium. Cells expressing different receptor types displayed different distribution patterns. In addition, sets of several reactive neurons within the same laminar zone were found to be arranged in an orderly fashion and were positioned at well-defined intervals. These results indicate that the localization of sensory neurons expressing a distinct receptor type is under stringent control leading to characteristic expression patterns.