The use of fuel with a low amount of sulphur cannot be delayed in the major European cities and the use of purposely transesterified and refined seed oils - named biodiesel -appears to be the most convenient solution. This investigation presents the results of a wide experimental campaign carried out on an IDI engine and aimed at evaluating the overall performance, the emissions and the combustion trends observed with the new fuel. Pure biodiesel and blends of biodiesel combined with 10% methanol have been evaluated in detail. A remarkable reduction of smoke emerged from both solutions. When the injection timing was advanced, better results were obtained, thus confirming the advantage of these fuels.