Rasmussen's encephalitis (RE) is a rare condition characterized by drug-resistant seizures, recurrent status epilepticus and progressive lateralized neurological deterioration. There is evidence of autoimmune involvement in the pathogenesis. We investigated the presence of anti-GluR3 antibodies against peptides A and B in patients with RE (n=11), partial and generalized epilepsy (n=85) and other neurological diseases (n=30). The antibodies were specific for epilepsy and are thus not a marker of RE, while particularly high antibody titers characterized a subgroup of non-RE patients with "catastrophic" epilepsy. Antibodies against GluR3B peptide were significantly associated with frequent seizures compared to occasional or drug-controlled seizures.