This paper examines the effects of using ethanol, as a replacement of lead additives in gasoline, on exhaust emissions of a typical SI engine. The ethanol was blended with a base unleaded fuel in three ratios (10, 15, and 20 vol.%). CO, HC, and NOx emissions were evaluated at a wide range of engine operating conditions using an engine dynamometer set-up. The results of the ethanol blends were compared to those of the base fuel and of a leaded fuel prepared by adding TEL to the base. With respect to the base and leaded fuels, the addition of ethanol decreased the CO emissions significantly. Low ratio ethanol blends increased the HC emissions and decreased NOx emissions at most operating conditions. On the other hand, higher ratio ethanol blends resulted generally in similar or lower HC emissions, and similar or higher NOx emissions. The emissions results for the leaded fuel were comparable to those of the base fuel at most operating conditions.