In Germany 100.000 tons of biodiesel (rape seed oil methylester, RME) were produced in 1998. 200.000 tons are expected in 2000. Therefore, it is necessary to judge the environmental and health effects deriving from the use of RME in combustion engines. The analysis of particle size and particle number distributions of diesel soot and the determination of its mutagenic effect were investigated. Additionally, emissions of ozone precursors were analyzed for both fuels. Finally, regulated and some important non-regulated emissions from different blends of RME and fossil diesel fuel were determined.