The present work describes an experimental investigation concerning the electric energy generation using blends of diesel and soybean biodiesel. The soybean biodiesel was produced by a transesterification. process of the soybean oil using methanol in the presence of a catalyst (KOH). The properties (density, flash point, viscosity, pour point, cetane index, copper strip corrosion, conradson carbon residue and ash content) of the diesel and soybean biodiesel were determined. The exhaust emissions of gases (CO, CO2, CxHy, O-2, NO, NOx and SO2) were also measured. The results show that for all the mixtures tested, the electric energy generation was assured without problems. It has also been observed that the emissions of CO, CxHy and SO2 decrease in the case of diesel-soybean biodiesel blends. The temperatures of the exhaust gases and the emissions of NO and NOx are similar to or less than those of diesel. (c) 2006 Elsevier Ltd. All rights reserved.