The olfactory epithelium of developmental stages from yolk sac larvae to adults of plaice, Pleuronectes platessa L. (Pisces: Pleuronectidae) and Dover sole, Solea solea (L.) (Pisces: Soleidae) was examined using scanning electron microscopy (SEM). Two ciliated cell types and a microvillar cell are present in both species soon after hatching and persist into adulthood. In juveniles and adults of plaice, there were significantly higher densities of ciliated sensory cells in the eyed side of the fish than in the blind side over all regions of the olfactory lamellae. Densities of microvillar cells were an order of magnitude less than those of ciliated cells in regions on the wider part of the lamellae, with no significant difference between organs in most of these regions. On the narrow part of the lamellae, densities of microvillar cells were significantly higher than on the wide part, and significantly higher in the eyed side organ. In sole, ciliated cells were significantly more dense in the blind side organ in three of the four regions examined in this species. In contrast, microvillar cells showed a similar pattern to that in plaice, being significantly more dense in the eyed side organ in two of the four regions. Comparisons between the species showed significantly higher densities of both cell types in sole, microvillar cells being an order of magnitude denser in comparable regions on the lamellae. In addition, the total area of the olfactory lamellae is around three times greater in sole. These data point to a possible morphological basis for the enhanced olfactory capabilities of sole apparent from behavioural studies.