The gracile and internal and external cuneate nuclei of four adult cats were studied, using recently developed stereological techniques. The length, volume and position of the nuclei in relation to the level of obex were calculated, as well as the number of neurones, the neuronal density and volume of the three nuclei and different regions in the gracile and internal cuneate nucleus. Material processed for GABA immunocytochemistry was used in order to compare GABAergic and non-GABAergic neurones. The results demonstrate variations in the same nucleus in different animals, and in the nucleus of the left and right sides of the same animal. The same nucleus can vary up to 4 mm in its rostrocaudal position in relation to the obex. The mean sizes of the gracile, internal and external cuneate nuclei are 4.2, 8.4 and 5.6 mm3, respectively and their mean neuronal numbers are about 52,000, 76,000 and 33,000, respectively. The neuronal density was highest (12,907 cells/mm3) in the gracile, and lowest in the external cuneate nucleus (5987 cells/mm3). The external cuneate nucleus had a larger relative volume (7.9%) occupied by nerve cell bodies compared with the two medial nuclei (5.1% and 5.8%). In the gracile and internal cuneate nuclei, the GABAergic neurones constituted 28% and 25% of the whole population, respectively, while the external cuneate nucleus was devoid of such cells. All the nuclei contained GABA-positive boutons, however. The mean volume of the GABA-stained neurones in the gracile nucleus was 2319, and internal cuneate 3065 microns3, while the corresponding volume of unlabelled neurones in the gracile, internal and external cuneate nuclei was 3745, 8147 and 13318 microns3, respectively. When cyto-fibro-architectonic characteristics were used to subdivide the gracile and cuneate nuclei into rostral, middle and caudal regions, and the data of the three compartments compared, it was found that in both nuclei the middle region had the highest neuronal packing density, and the caudal region the largest mean nerve cell volume.