Since 1984 the Landesanstalt fuer Umweltschutz Baden-Wuerttemberg has established a statewide system of 60 permanent research plots for biomonitoring long term effects of air pollution on relatively undisturbed forest ecosystems. Among general vegetational analyses the vitality of plants in the herbaceous layer and the canopy is assessed. Special attention is paid to lichens as well as to Galium odoratum, Vaccinium myrtillus and beech (Fagus sylvatica). In addition leaves of beech and fir (Abies alba) are analysed for contents of lead and cadmium. The results show that there are two types of more strongly affected plots: Some are exposed to higher levels of air pollution and consequently show severe pollution effects even though the environment conditions may be favourable for forests. Others are so sensitive that effects occur inspite of lower levels of pollution. In these cases the balance is apparently more easily disturbed because of acidic soils and less favourable climate. (orig.).