In order to elucidate the morphological correlates of bladder-rectal dysfunctions in Shy-Drager syndrome, the sacral spinal cord was cytoarchitectonically studied and 3 groups of sacral motor neurons, the posterolateral motor neuron column (PL), inferior intermediolateral nucleus (IML) and cell group X of Onuf (Onuf), were morphometrically quantitated at the S3 level (5 cases), after which the results were compared with those from amyotrophic lateral sclerosis (5 cases) and an age-matched control group (4 cases). The sacral autonomic preganglionic nucleus of IML was localized chiefly in the S3-4 segments and was maximally developed in the caudal one-third of S3. The cell group X of Onuf was localized between the middle of S2 and the rostral one-third of S3 as a longitudinal slender column in the ventral horn. Between these two nuclei at the rostral S3 level, a connecting cellular bridge of neurons of intermediolateral cell type was identified. Morphometry disclosed a marked deprivation of IML, Onuf and somatic motor neurons in Shy-Drager syndrome and a severe loss of somatic motor neurons and a modest deprivation of IML neurons in ALS. These results imply that these two disorders distinguished by different clinical manifestations share a common loss of somatic motor and parasympathetic motor neurons at least in the sacral cord. There are, however, certain gradients in the severity of involvement in these heterogeneous cell groups.