The rapid quantification of paraquat in body fluids is of undoubted value in both initial assesment as well as the immediate prognosis of acutely poisoned patients. A 20-year-old woman ingested a mouthful of paraquat. Serum and urine paraquat levels were measured colorimetrically for 48 hours after identifying the presence of paraquat in her urine by a Paraquat test kit. At that time her survivability was considerd to be over 50% according to Proudfoot's scale of time related measured serum paraquat levels. Five days after admission, she began to cough but her chest x-ray picture was normal. However, she persisted to cough and subsequent chest x-rays showed fine reticulonodular densities in both upper and lower lobes. Twenty days after admission, she .was clinically well, and not deteriorated radiologically. Therefore, respiratory function tests were under-taken. They showed reduced lung volume, moderate reduction in ventilatory capacity, and a diffusion defect (DLco: 27% predicted value). Twenty four days after admission, the patient was discharged in good condition except for the sequale of lung involvement. Six months later, she was re-examined and found to be healthy with a large regression of lung lesions on her chest x-ray.