The spatial distribution of chemosensory afferent terminals within glomeruli, with respect to their peripheral origin, was investigated using differential staining of afferents in the cockroach. In all glomeruli, the axon terminals of afferents originating from the more distal regions of the flagellum tended to occur in the more distal regions of the glomeruli, relative to the axonal entry side. Afferent terminals tend to be spatially separated, on the basis of their circumferential origin on the flagellum, in pheromone-receptive glomerular complexes and posterodorsally located large glomeruli; however, they were randomly scattered in anteroventrally located small glomeruli. These results revealed that the location of afferent terminals strongly reflects the three-dimensional position of their olfactory receptor neurons in pheromone-receptive glomeruli, but the relationship is weaker in other glomeruli.