Since MTBE and its metabolite, TBA, coexist under certaincircumstances, the mixture toxicity of MTBE and TBA has tobe understood. Since the soil can be the first medium in whichoxygenate contamination occurs from the spillage of the un-derground storage tanks and oxygenate-contaminated watermay be utilized for agricultural purposes, the toxicologicalinformation on the effect of fuel oxygenate on plant growthshould be valuable.