The authors report three cases of syndromes of the red nucleus - two cases of superior syndromes and one of inferior syndrome, Claude's form. The anatomy and physiology of the nucleus ruber is briefly reviewed. The changes in the muscle tonus following experimental lesions of that nucleus are emphasized. Damage to the parvicellular, rostral portion (neorubrum) leads to a decrease of tonus caused by release of the tonus-inhibiting magnocellular portion; the destruction of this latter is followed by hypertonus, caused by the free action of the dynamogenic rhombencephalic nuclei. In order to correlate the experimental and anatomo-clinical facts, the authors recall De Giacomo's concept about the pathologic topography of the rubral syndromes: in the Benedikt's form, the lesion would be located in the paleorubrum; in the Claude's and superior syndromes, the neorubrum would be the portion involved. The authors also discuss the problem of the hyperkinesias, emphasizing their "intentional" character; they recall the existence of reciprocal, direct and indirect, rubrocortical connections and stress the fact that the red nucleus is a station in the Bucy's circuit of the intention tremor. The reports of rubral syndromes are scarce; in the Brasilian literature the authors found 5 cases reported, including 4 cases of the Benedikt's form. Commenting their cases, the authors emphasize: a) the syphilitic etiology of the lesions, mesenchymatous in one case and parenchymatous in two; b) the presence of marked hypotonia in two cases and the normality of the muscle tonus in the other one; c) the absence of electroencephalographic abnormalities in one case of superior rubral syndrome and one case of Claude's syndrome; d) the discordance of the vestibular reactions evidenced in one case; e) disturbances in the thermic regulation in case 2, which are imputed to the associate lesion of the mamillotegmental tract and/or the dorsal longitudinal fasciculus; f) the association, in one case of superior rubral syndrome, of rhytmic myoclonus in the soft palate, pharynx and larynx, probably owing to lesion of the central tegmental tract or of the origin of its rubrolivary fibers.