The aim of this study is to experimentally investigate the effects of blends containing various alternative fuels and diesel fuel on the performance and emissions of a diesel engine. The considered parameters are brake power, specific fuel consumption and thermal efficiency as well as carbon monoxide, hydrocarbon and nitrogen oxide emissions. Blends of biodiesel, ethanol, methanol and vegetable oil with diesel fuel, each containing 15% alternative fuel in volume, were prepared. Then, these blends were tested in a naturally aspirated, direct injection diesel engine. The test results obtained with these blends were compared with those obtained with diesel fuel. It was found that the tested blends yielded usually different performance and emission characteristics compared to diesel fuel. The biodiesel blend resulted in performance parameters very close to those obtained in the use of diesel fuel. Ethanol and methanol blends yielded lower brake power, while they resulted in higher specific fuel consumption and lower carbon monoxide emissions. On the other hand, the vegetable oil blend yielded lower carbon monoxide emissions, while it caused only slight changes in the performance parameters. (C) 2011 Elsevier Ltd. All rights reserved.