BACKGROUND: Brazil is one of the largest exporters and producers of ethanol. The local commercialization of flex fuel cars (vehicles that can run with pure gasoline or pure ethanol or the mixed gasoline) increases annually. Biofiltration technology can treat ethanol and gasoline vapors, mineralizing contaminants. The aim of this research was to evaluate biofiltration technology treating ethanol-gasoline vapor mixtures, considering different proportions of the two pollutants and of the mixture in increasing concentrations. Two bench scale biofilters (System 1 and System 2) were evaluated, each of 2.72 L. Packing material was a mixture of compost and granulated rubber tire at 2:1 (v/v). The gas flow rate was 450 mL min-1, resulting in an empty bed retention time of 6.04 min. Inlet pollutant concentration ranged from 1.3 and 59 g m-3 (System 1) and 1.25 g m-3 and 55 g m-3 (System 2). Gasoline/ethanol ratios applied were (%): 80/20, 60/40, 40/60, 20/80 and 100% of ethanol. RESULTS: Removal efficiency and elimination capacity increased with ethanol load augmentation. During the six phases of study the removal efficiency average remained above 70% and the maximum elimination capacity achieved was 587 g m-3 h-1 (biofilter system 1) with neat ethanol. CONCLUSIONS: This study showed that biofiltration is an excellent option for gasoline amended ethanol vapors treatment. Copyright (c) 2012 Society of Chemical Industry