Five cases of encephalopathy due to intravenous penicillin treatment (penicillin G sodium in 4 cases, oxacillin in 1) are reported in 5 uraemic patients. The first abnormalities noted were decreased consciousness and myoclonic jerks (3 cases), followed by seizures and coma (2 cases). Lumbar puncture and cerebral computed tomography gave normal results. Electroencephalograms showed diffuse sharp and slow activities over the brain areas. The diagnosis was confirmed by the high blood levels of the penicillins. Three patients recovered after discontinuation of the drugs; two patients died in status epilepticus and coma resistant to all treatments.