We assess the environmental health impact and policy implications of the widespread addition of methyl tert-butyl ether (MTBE) as a chemical that is used as an oxygenate to much of the gasoline supply in the United States. Initial concerns about short-term and long-term adverse health consequences following the substantial increase in MTBE use in the winter of 1992-1993 have been supplemented by the discovery in 1996 of what is now relatively widespread contamination of groundwater. We identify 14 governmental initiatives during the 10-year period 1989-1999 in which the potential adverse consequences of MTBE were considered and a nearly identical research agenda was proposed. The lessons from the ongoing MTBE episode show that: (a) research should precede rather than follow environmental health policy decisions; (b) the extent of potential human and environmental exposure should be an important criterion in determining the amount of information needed before making an environmental policy decision; (c) a better understanding of nonspecific human symptoms associated with environmental exposures is needed; (d) the boundaries between the US Environmental Protection Agency program offices should be as porous as the boundaries between environmental media; (e) the US Environmental Protection Agency needs to focus more on public health rather than on legal approaches to environmental management; Cf) it is more difficult to remove a chemical once it is in commerce than it is to prevent its use; (g) resolution of uncertainty is best accomplished through research rather than through repetitive review; and (h) better tools are needed to evaluate risk/risk trade-offs. The ongoing replacement of MTBE by other, less well. studied oxygenates such as tertiary amyl methyl ether indicates that these environmental public policy lessons have not been learned.