The toxic action of thallium was first noted in 1865 by Lamy.1Thallium has had its widest use in recent years as a rodent poison. For this purpose it is usually mixed with barley and distributed in animal runways. The present report deals with eleven cases of poisoning from the use of barley mixed with thallium sulphate. After the barley had been ground, tortillas (a Mexican bread made by mixing flour and water and rolling the dough into thin cakes) were made from the whole grain. These patients gave a uniform history of onset of symptoms twenty-four hours after partaking of the tortillas. The first symptoms noticed were a tingling sensation and pains in the hands and feet, followed by severe paroxysmal abdominal pains and vomiting. No diarrhea was observed. Shortly after the first manifestations, weakness of the extremities developed. This weakness did not involve any particular muscle group