Acute isoniazid overdose is a relatively uncommon but potentially life-threatening event. Isoniazid overdose should be suspected in any patient with repeated seizures, coma and metabolic acidosis of uncertain etiology. The effective antidote for acute isoniazid- induced neurotoxicity is known to be pyridoxine. We report a 4-month old boy who showed repeated seizures, coma, metabolic acidosis and hyperglycemia from an accidental isoniazid overdose(100 mg/kg). This boy was recovered completely by the pyridoxine treatment with a dose of equivalent to the amount of isoniazid ingested.