The recent furor over paraquat contamination of Mexican marijuana imported into this country has involved some controversy over how much of the herbicide survives pyrolysis in marijuana cigarettes and how much danger the unknown amount of paraquat poses to the Cannabis smoker [1–5]. While much is known about the pulmonary toxicity of ingested paraquat [6–9], little is known about the toxicity of inhaled paraquat, and even less about the physiological activity of its pyrolysis products.