The ethers of ethylene and diethylene glycol have been extensively used in industry for the past fifteen to forty years. Though developed specifically for the coating industry, their high solubility in water and their compatability with organic solvents have led to their use as solvents in dyes, insecticides and pesticides, liquid soaps, cleaning solutions and in cosmetics. They are also used as chemical intermediates and as diluents for hydraulic brake fluid. Available data indicate that the glycol ethers, in general, have a low to moderate degree of toxicity. The majority of these compounds are only slightly irritating to the skin, though most are readily absorbed percutaneously. Eye contact produces moderate irritation. Prolonged or repeated inhalation of the vapors may cause irritation and adverse systemic effects, however the relatively low volatility of these ethers should prevent exposure to toxic concentrations at normal temperatures. Since most of the toxicity data available have been generated 15 to 20 years ago, at different times, in different laboratories and by various investigators, comparison of the toxicity between the different ethers is very difficult because of inter and intra-laboratory variations. Therefore, several toxicity studies were designed in our laboratory to specifically study the comparative toxicity of nine glycol ethers. This report describes the results of acute oral LD50 studies in rats and mice.