Since its introduction in 1952, isoniazid has remained one of the drugs of choice in the treatment and prophylaxis of tuberculosis. In populations with a high prevalence rate of tuberculosis or suicide rate, acute ingestion of isoniazid has occasionally been reported. Acute intoxication by isoniazid is known to cause symptoms of seizures, metabolic acidosis, coma, and even death. These clinical symptoms, however, are not well recognized by physicians in Taiwan, even though the prevalence rate of tuberculosis is relatively high here. This report concerns the case of a 25-year-old female with a past history of tuberculosis who presented with the symptoms of refractory seizures, metabolic acidosis and deep coma after intentional ingestion of some unknown drug. Although implicating agents were not recognized initially, she was successfully revived with basic resuscitation, anticonvulsants and correction of metabolic acidosis. A review of her history revealed that her ingestion of five grams of isoniazid in this case was responsible for the entire clinical spectrum. Given easy access to isoniazid in Taiwan, a diagnosis of isoniazid poisoning should always be considered in patients who present with the classical symptoms of refractory seizures, metabolic acidosis and coma.