The effects of rapid rectal diazepam introduction (DZP test) were investigated in 43 patients (age range 5 months-14 years) with electrical status epilepticus (ESE) undergoing EEG monitoring. A remission of the paroxysmal activity was obtained in 58% of cases, a negative response in 42%, particularly in hypsarrhythmic patterns. DZP test responders were aged over 12 months with organized paroxysmal EEG patterns, in particular with ESE during sleep (ESES). The patients who responded to the DZP test underwent short cycles (3-4 weeks) of relatively high dosage DZP (0.5-0.75 mg/kg). The response to treatment was positive in 64%, particularly in ESES conditions. 56% of responders to the DZP test but not to DZP therapy (five out of nine patients) presented a significant mental retardation; maturational factors were also likely to be present.