Xanthona parietina thalli were collected from a ‘clean-air’ location and from a polluted area. Ramalina duriaei thalli were collected from the same ‘clean-air’ location and some thalli were transplanted to air polluted locations, where R. duriaei no longer occurs. The effects of air contaminants on these two lichens were compared under controlled laboratory conditions and in field experiments. Air contaminants and exposure to bisulphite ions had little or no damaging effect on X. parietina, whereas severe damage was caused to R. duriaei, as judged by chlorophyll degradation, autofluorescence of photobionts, photosynthetic activity, membrane integrity and ATP content. The different responses presented confirm the sensitivity of R. duriaei and resistance of X. parietina to air pollution.