The huge number of species and reactions involved in the degradation of organic compounds does not permit explicit treatment in regional models, the use of condensed mechanisms is necessary. With increased knowledge about biogenic VOC chemistry, updates of the organic chemistry have become necessary. Geiger et al. (2003) introduced a RACM mechanism with improved isoprene and biogenic VOC chemistry. To understand the mechanisms, case studies were performed: A box-model-intercomparison and MCCM (Grell et al., 2000) cross-validations. Focusing on ozone, differences were rather small. In the regional applications, RADM2 produced the highest daily ozone concentrations. Intercomparisons with measurements result in good correlation.