A number of possible displacing agents have been tested for their ability to release extracellular bound lead from Cladonia portentosa. Metal cations (Ni and Cu), thiol–rich reagents (glutathione, ammonium pyrrolidinedithiocarbamate) and some chelating agents (EGTA, EDTA at pH 9·5 or pH 2·7) were ineffective or caused membrane damage. Disodium EDTA at pH 4·5 was found to be an effective displacing agent, although the Na caused some release of intracellular K without membrane damage. This displacement procedure showed that no Pb suppliedin the laboratory entered the protoplast in 2 h. The effect of Ca, Cu, Pb, and Sr on membrane integrity was investigated.