From 16 patients, presenting diseases of the nervous system, porbably of viral etiology, cerebrospinal fluid and/or stool samples have been collected for virus isolation in cell culture and in sucking mice. The technical methods adopted have been previously related by one of us. Enterovirus have been isolated from stools of 3 patients: virus Coxsackie A-1, from a patient with encephalitis, virus Coxsackie A-1 and poliovirus type 3, from a patient with meningo-encephalitis; and poliovirus type 3, from a patient with meningo-myelitis. High titer of neutralizing antibodies against poliovirus type 3 was found in the last case, the only positive case in which serum was collected. There is a possibility that the poliovirus isolated from the patient with meningo-encephalitis was originated from the previous Sabin vaccination. The etiological significance of the isolations of Coxsackie A-1 virus in the first two cases was considered insufficient, as it was not possible to evaluate the presence of homotipic neutralizing antibodies.