Since May 1995 an air quality bio-assessment by epiphytic lichens has been carrying out within Canton Ticino. The research method is based on the "lndex of Atmospheric Purity" (I.A.P.). The worst air quality (O < I.A.P. < 30) was detected in the centre of the main towns and in the surrounding areas while the highest values of the I.A.P. (I.A.P. > 50) were observed in the Western part of the Canton, on mountain belt. Moreover, the Ecological lndices of Wirth have been evaluated: through a floristic analysis it has been possible to check the influence of pH and nitrogen enrichment of substrata on lichen distribution. Our observations confirm previously reported data: pH driving forces are a compromise among secondary substratum eutrophization (increasing pH), acid rains and tree trunk essudates. Considered this, till now, the Canton Ticino does not show any significative difference with the contiguous ltalian zones. The research is still in progress.