A retrospective study of 113 patients treated with a sustained-release form of valproate (SRF-VPA), known as the "chrono" formulation in most European countries, led to the following conclusions: Patients treated with the old VPA formulation could immediately receive the same daily dosage of SRF-VPA without loss of seizure control when administered as a single evening dose. The tolerability of SRF-VPA was good and twice or single daily dosing was preferred by all our patients. Whether or not SRF-VPA should be used as first or second-line treatment in partial seizures that do or do not secondarily generalize is unclear. Our study demonstrates that the efficacy of SRF-VPA is comparable with that of other major antiepileptic drugs such as carbamazepine (CBZ). In refractory seizures, the combination of SRF-VPA and CBZ seemed to be the most satisfactory treatment. Based on these results SRF-VPA is a promising drug for all types of seizures even in low daily dosage, but further clinical work is required to confirm our observations.