 Most patients are prescribed valproate as their first antiepileptic drug. It is unknown which is the best second-line drug when patients do not become seizure free on valproate. This has led the Dutch Epilepsy Clinics Foundation SEIN to start the SLICE study. Adult patients with partial andor tonic-clonic seizures, insufficiently responding to valproate, are recruited for this study. These patients are randomized to receive one of three other drugs. Patients wil initially use this drug next to valproate. Neurologists of more than 20 general hospitals en neurologists of SEIN are participating in this study. 