Shortage of fossil fuels requires from scientists to undertake investigation focused on applying alternative, renewable based fuels to a reciprocating engine. Among others, alcohols: methanol and ethanol are proposed as satisfactory fuels, that would be applied either as single fuels or blended with gasoline o diesel fuel. The paper describes impact of both methanol and E85 (85% ethanol and 15% gasoline) as additional fuels added to a diesel fueled engine on its combustion characteristics and exhaust toxic emission. These fuels were added by injection into an intake manifold in amounts expressed by their energy percentage of 20%, 50%, 75% and 90% with respect to total diesel fuel-methanol or diesel fuel-E85 blends. The tests in a compression ignition engine contained analysis of heat release rate and combustion parameters as well as analysis of exhaust toxic emission NOx, THC, CO and soot. It was observed that with increase in methanol or E85 peak combustion temperature decreases as well as temperature of the mixture at the end of compression stroke that affects combustion duration. For methanol or E85 two characteristic peaks in the heat release rate profile were observed. The first peak represents burning the diesel fuel and the second burning methanol or E85. Hence, diesel fuel injection timing should be corrected, if alcohols, even in small amounts, are applied. Furthermore, as advantage, slight increase in brake efficiency was observed. Next, radical reduction in soot, particularly at 50% alcohol (methanol or E85) addition was also managed as important advantage. On the other hand, increase by 16% in NOx emission was observed, while 20% methanol or E85 were added. Summing up, addition of methanol or E85 to the diesel fueled engine is justified, however, it significantly changes entire combustion process. Especially, intensive research should be undertaken on reducing higher NOx emission. (C) 2015 Elsevier Ltd. All rights reserved.