Serum anticonvulsant determinations made possible the identification of an unusual cause of status epilepticus and assisted with appropriate therapy in an epileptic patient with second-degree burns. The seizures were associated with a serum phenytoin concentration of 3.5 mug per milliliter. This suboptimal concentration of drug developed despite continuation of the patient's customary oral dose of phenytoin led to the conclusion that the unexpected decrement in serum anticonvulsant concentration was related to an experiment in absorption of that drug, possibly caused by the concurrent administration of oral oxacillin.