Lichen thalli were soaked in water adjusted to pH 1.0-12.0 to study the influence of different pH conditions on the integrity of the photobiont's chlorophyll. The ratio OD 435 nm/OD 415 nm, used to estimate the chlorophyll degradation, decreased after a 30 min treatment in water acidified to pH 1.0-2.0. Thalli were exposed to solutions containing potassium or heavy metal chlorides, sulfates and nitrates under acidic conditions, all of which exerted different degrees of chlorophyll damage. The chlorophyll integrity was especially affected following treatment of the thalli with Cu, Zn, Mn, Pb, Fe(II) and Fe(III) salts under pH 2.0. Under the same pH, SO42- combined with K+ proved more harmful to the photobiont chlorophyll than Cl- anions. After a treatment with CuCl2, a very low OD 435 nm/OD 415 nm ratio was obtained.