The pathophysiology, symptoms and treatment of paraquat intoxication, primarily from oral ingestion, and the pharmacology and pharmacokinetics of paraquat are reviewed. Toxicity has occurred after topical application, oral ingestion or inhalation of paraquat. Systemic toxicity has not been reported from smoking of paraquat-contaminated marijuana but heavy abusers of contaminated marijuana may experience coughing, hemoptysis and mouth irritation. Following ingestion of 30 mg/kg or 50 ml of a 21% (w/w) solution of paraquat (as the base), hepatic, cardiac or renal failure or death may occur. Smaller doses (greater than or equal to 4 mg/kg of paraquat base) may cause respiratory distress, renal dysfunction or, occasionally, jaundice or adrenal cortical necrosis. When paraquat ingestion is suspected, the drug should be removed immediately from the gastrointestinal tract by gastric lavage or by whole-gut irrigation. Adsorbents such as Fuller's earth, bentonite or activated charcoal may be used during gastric lavage. Combined use of forced diuresis (with furosemide, mannitol and i.v. dextrose in water or normal saline), hemodialysis or hemoperfusion is recommended until the compound cannot be detected in body fluids or the dialysate. Immediate and effective treatment is necessary to prevent systemic toxicity or death from paraquat intoxication.