To elucidate an effective therapeutic strategy for 'ESES syndrome', epilepsy with electrical status epilepticus during slow sleep (ESES) and its related epileptic disorders, we studied the effect of treatment on the EEG pattern of continuous spike-waves during slow wave sleep (CSWS) in 15 afflicted patients. Basically performed in the following order, the employed therapies included (1) high-dose valproate (VPA) therapy (serum level >100 microg/ml); (2) a combination therapy of VPA and ethosuximide (ESM); (3) short cycles of high-dose diazepam (oral or intrarectal DZP, 0.5-1 mg/kg per day for 6-7 days); and (4) intramuscular synthetic ACTH-Z therapy (0.01-0.04 mg/kg per day for 11-43 days). Regarding the initial EEG effect, a remission of CSWS was achieved by high-dose VPA therapy in 7 of 15 trials (47%), by the combination therapy of VPA and ESM in 3/7 trials (43%), by short cycles of high-dose DZP in 2/4 trials (50%), and by ACTH-Z therapy in 2/5 trials (40%). A permanent remission of ESES syndrome was achieved by high-dose VPA therapy and/or combination therapy of VPA and ESM in 10 patients (67%). The effects of short cycles of high-dose DZP and ACTH-Z therapy were at best temporary. Our strategy for the treatment of ESES syndrome is therefore considered valid.