A nonhydrostatic mesoscale model which is coupled with a transport and diffusion model and the gas phase mechanism RADM2 is used to study the influence of biogenic volatile organic compounds (VOC) emission on the ozone concentration during episodes of high air temperatures in the state of Baden-W¿rttemberg, Germany. All model parts, including the determination of the biogenic VOC emissions, are run in a coupled mode. The results of the model simulations are compared with observations for a summer smog episode which occurred in August 1990. Simulations which are carried out without biogenic VOC emissions show a maximum difference in the ozone concentration of 18 ppb, while the maximum ozone values are of the order of 100 ppb. This shows that the biogenic VOC emissions play an important role when high temperatures are present in Baden-W¿rttemberg. Simulations which are carried out with homogeneous terrain height show differences in the biogenic emissions caused by changes in the temperature distribution. Large differences are also found for the concentration distributions. The differences in the results which are obtained with and without biogenic VOC emissions are decreasing; the maximum difference is about 10 ppb. This demonstrates the necessity of a sufficient treatment of topographic effects in the regional scale. ¿ American Geophysical Union 1995