Butanol, which can be produced from biomass, has been suggested as an alternative to ethanol, due to its higher energy density, lower oxygen content and more favorable hygroscopic and corrosive properties. In the Czech Republic, E85 is widely sold at fuel stations and used in ordinary vehicles, both with and without aftermarket control units. This work investigates the potential of ordinary automobiles to run on butanol, and the associated effects on exhaust emissions under real driving conditions.A Škoda Felicia car with a throttle body injection and a Škoda Fabia car with a multi-point port injection have been run on gasoline and its mixtures with up to 85% volume of ethanol, of n-butanol, and of isobutanol (2-methyl-1-propanol). An auxiliary control unit has been used with higher alcohol content. On each fuel, each car was driven 5-6 times along a local test route. The emissions of gaseous pollutants and other parameters were measured by a portable on-board emissions monitoring system.The results suggest that the engine control units of both cars prolonged the fuel injection pulse width allowing the engines to operate on all tested mixtures. On the throttle body injected engine, oscillations of air to fuel ratio to both rich and lean mixture compositions were observed for all alcohol containing mixtures, especially for mixtures with high butanol share. This resulted to significant increase of nitrogen oxides emissions with a lack of significant decrease of carbon monoxide. On the engine with multipoint injection system, only minor general shift of air to fuel ratio was observed, with minor changes of air to fuel ratio peak to peak value. This resulted in less apparent changes of gaseous pollutants production.