In the Czech Republic, there are forest ecosystems under various stress factors (acidification, cutrophization, Al-phytotoxicity, deficiency of nutrients). Thus since 1988, intensive chemical research was conducted to clarify cause-effect relationships between air pollution and forest decline. Some smog episodes were detected and caused their visible injuries, especially in 1996. In this study cation leaching from Norway spruce canopy (Picea abies (L.) K a r s t.) is used as chemical indicator for direct or indirect impacts of acidic deposition. Tree canopy internal circulation of nutrient indicates and reflects the health and environmental conditions of spruce. The calculation of total acid deposition and tree canopy internal circulation of basic cations is described.