Methyl tertiary butyl ether (MTBE), a volatile oxygenate commonly used in fuels, is a frequent contaminant of some shallow groundwater. Based on limited reporting, concentrations of MTBE in drinking water were generally less than 10 μg/L but excursions up to 770 μg/L have been reported. Based on current MTBE toxicological data with emphasis on carcinogenic potential, and reproductive and developmental effects, a maximum drinking water level of 100 μg MTBE/L is suggested. This recommended advisory level takes into consideration the equivocal evidence of the carcinogenicity of MTBE in humans and low potency in an oral exposure animal study. Definitive conclusions regarding health risks to the general population from MTBE contamination of drinking water are not possible due to a paucity of monitoring data. There is increased evidence of contamination of storm water and shallow groundwater from primarily, nonpoint sources. Considering MTBE mobility and stability in water, movement to deep groundwater and drinking water supplies seems probable. In light of projected increased MTBE use, there is a need for a more rigorous monitoring program to define the frequency of MTBE contamination of drinking water supplies and to develop risk management policies.