Twenty two epileptic patients, with daily seizures (5 had typical absences, 3 had psychomotor seizures, 5 had myoclonic absences, one had intentional myoclonia and 8 had Lennox syndrome) were treated with 7-nitro-5-(2chlorophenyl)-3H-1,4 benzodiazepine-2(1H)-one or Ro 5-4023. Twenty of these patients had received previous treatment with other anticonvulsivant drugs with no satisfactory results. A clinical and electroencephalographical longitudinal study was made on these patients. With the use of Ro 5-4023 the seizures were completely controlled since the first day in 14 patients; in 6 there was a rapid and significant decrease in frequency and intensity of seizures; in one, out of these 6, seizures disappeared during the second week of treatment. Recurrence of seizures were observed in 8 patients. The drug is effective in a large spectrum of generalized seizures (typical absences, myoclonic absences); partial seizures, in particular the psychomotor seizures of infancy with slow spike-waves; the severe epileptic encephalopathy of infancy, Lennox type; and the degenerative epileptic syndrome. Side effects due to the drug were present in 11 patients, being of short duration in 9. In two patients there was precipitation of generalized tonic-clonic seizures; anyhow it seems that the occurrence of this complication is more frequent when one uses other types of benzodiazepines. Electroencephadographic studies showed improvement of the previous abnormalities; there was disappearance or decrease of bilateral diffuse discharges, when spontaneous or provoked by intermitent light stimuli, onset of diffuse, fast rhythm, persistance or onset of slow focal abnormalities or irritative type of discharges.