A case report on a 13-year-old girl with idiopathic grand mal epilepsy who ingested 34 g carbamazepine (CBZ) and 80 mg clonazepam is presented. The patient survived but suffered severe temporary neurological toxicity characteristic of CBZ. CBZ was 79.6 +/- 2.8% bound to serum protein and carbamazepine-10,11-epoxide (CBZ-E) binding was essentially concentration dependent. CBZ and CBZ-E elimination half-lives were 26 and 16.5 h respectively. An inhibitory metabolic interaction with the co-ingested clonazepam is suggested.