The renewable nature and smoke emission advantage of the vegetable oil derived biodiesel fuels are making them an attractive alternative to fossil diesel fuel in compression ignition engines. The results of an experimental investigation on neat Jatropha and Karanja derived biodiesel in a turbocharged diesel engine are presented here. It is observed that the Jatropha and Karanja methyl esters (JME and KME) show 10.2% and 8.5% increase in peak cylinder pressure, 14 and 12 times lower unburnt hydrocarbon emissions and 85% and 92% lower smoke levels respectively as compared to fossil diesel fuel. Though, JME and KME exhibit better combustion, HC and smoke emission characteristics than diesel fuel there is some penalty in terms of fuel consumption and nitric oxide emission. © 2009 Combustion Institute. All rights reserved.