The content of eight heavy metals: Mn, Zn, Fe, Pb, Ni, Cu, Cr and Cd in the lichen Caloplaca aurantia growing on roof-tiles in urban, suburban and rural settlements in Israel has been evaluated. The data obtained and their statistical analysis indicated the following: (1) The content of all the above listed metals was generally higher in the lichen growing in 'town' than in 'village' areas; among these metals Ni and Zn were found most suitable for the distinction between 'town' and 'village' settlements. (2) Comparisons of the coefficient of variation of metal content values in 'town' versus 'village' furnished indications on the dispersion capacity of the metal particles. (3) Correlation analysis among the metals in 'town' and 'village' resulted in suggestive information on the emission sources. (4) Leaching tests indicated the tenacity of metal retainment and incorporation efficiency into the lichen tissue. Lichen species like C. aurantia, which grow both in 'clean' and metal contaminated areas are suggested as comparative monitors and for assessing periodical changes in metal output and concentrations.