Ethanol has been adopted as an alternative fuel to gasoline, especially in the Brazilian automotive market. The chemical properties of this fuel imposes difficulties for cold start and operation during the warm up period. To minimize this problem, up to the present ethanol–fuelled vehicles are equipped with a reservoir of gasoline, which is injected in small percentages in the cylinder at the start–up of the engine. This solution is not seen as a definitive one, because of the extra cost of the gasoline system, and because the results obtained are not entirely convincing. In this work MTBE (Methyl–t–butyl–ether) has been tested as an additive to ethanol to improve its cold start characteristics. Results have shown immediate start of the engine at temperatures as low as –6 degrees centigrade. Emissions levels for exhaust hydrocarbons, oxides of nitrogen and aldehydes were reduced, while carbon monoxide showed an increase for the ethanol–MTBE blend, when compared to pure ethanol. Fuel consumption was lower, torque hardly varied, and an increase in power was noticed when the vehicle was operated with blended fuel.