Removing lichen substances from dry lichen thalli using pure acetone is the least detrimental method. Measurements of properties strictly related to the photobiont, such as chlorophyll a fluorescence (Chl
F), are frequently used to verify acetone toxicity but they cannot reveal possible damage accumulated at the whole thallus level. Here, measurements of Chl
F have been integrated with others concerning the status of cell membranes and photobiont population (potassium leakage, malondialdehyde and photosynthetic pigment content). Dry thalli of Flavoparmelia caperata, Parmotrema perlatum and Xanthoria parietina were subjected to sequential acetone washings according to standard protocols. Membrane permeability was assessed before and after the washing treatment, and after a recovery period of 48 hours. Measurements of Chl
F were taken in a parallel experiment. Acetone washings increased potassium leakage in all the species from 3·9 to 6·6 times greater than the control level. After recovery, only P. perlatum returned to the control level. Chl
F was affected only in F. caperata, with a 20% decrease in F
m which had not fully recovered after 48 hours. There was neither an increase in lipid peroxidation of membranes nor a change in the photosynthetic pigment content. The sensitivity of F. caperata to this method and the impact of the results on its future application are discussed.