A 49-year-old male chemical industry worker was admitted to intensive care with a 24-hour history of respiratory failure, vomiting, headache, stupor, arterial hypotension, and cyanosed face and limbs. He had acute haemolysis (3.9 g/L plasma haemoglobin concentration) and 30% methaemoglobinaemia. Whereas the search for alcohol, barbiturates and opiates was negative, benzodiazepines and tricyclic antidepressants were present. The patient was in fact being treated with fluvoxamine, amitryptiline, and alprazolam. As the clinical and biological signs suggested chlorate poisoning, chlorate was looked for by using an aniline color reaction. It was found in gastric content and urine. Treatment consisted in mechanical ventilation, vasoactive amines, methylene blue, plasma exchange, exchange transfusion, and haemodialysis. Despite this, the patient had several cardiac arrests and refractory metabolic acidosis. He died 12 h after his admission. Specific ion chromatography was used afterhand to assay the chlorate in various body fluids. The technique was based on a separation on an ion exchange Dionex® AS 12A column coupled with conductivity detection. A quantitative estimation was carried out by using external calibration with a four-point calibration curve which was linear between 1 and 15 mg/L. The measured plasma levels of chlorate were 78 and 29 mg/L respectively before and after exchange transfusion. Gastric-lavage liquid contained 1300 mg/L of chlorate and urine 4300 mg/L. Ion chromatography, which is routinely used in environmental studies helped to confirm a massive oral intake of chlorate by measuring the corresponding blood and urine chlorate concentrations, data which had only rarely been reported previously.