Thalidomide was originally synthesized and tested as a sedative, hypnotic and antiemetic; however, after its teratogenicity was noted its use for treatment of neurological and psychiatric disorders was abandoned. We studied the potential anticonvulsant effect of thalidomide: Different doses of thalidomide were tested against seizures induced by 50 mg/kg or 70 mg/kg of pentylenetetrazole (PTZ); the anticonvulsant effect of thalidomide was also compared with that of valproic acid. Seizures and latency time were individually recorded. Thalidomide in low doses (5-10 mg/kg) prevented seizures in all animals treated with 50 mg/kg PTZ; also, in a dose-dependent manner thalidomide inhibited seizures in rats exposed to a high dose of PTZ (70 mg/kg); thalidomide exhibited an anticonvulsant activity similar to that of valproic acid. Thalidomide is an effective anticonvulsant, and further studies on this potential antiepileptic substance seem warranted.