Acute experimental toxicity studies of cesium (7440462) and rubidium (7440177) compounds were carried out. Single dose oral LD50, primary skin irritation index, degree of eye irritation, and skin allergic sensitization potential procedures were used. Compounds studied were cesium-hydroxide (1308470), 50 percent cesium-hydroxide and 50 percent potassium-hydroxide (1310583) mixture, potassium- hydroxide, cesium-iodide (7789175), rubidium-hydroxide (1310823), and rubidium-iodide (7790296). Data indicated that the hydroxides of cesium and rubidium were more toxic than the iodides. Cesium- hydroxide, potassium-hydroxide, and rubidium-hydroxide are strong alkalies, and contact with the eyes or skin should be avoided.