A secreted urease from the lichen Evernia prunastri thallus has been purified from the media in which thallus samples were floated for 1 h in the dark. This enzyme is a glycoprotein which contains 845 residues of galactose per molecule of protein. The Km of this enzyme has been estimated as 3.45 mM for urea. The enzyme is activated by atranorin, the only phenol which dissolves in the incubation media. This phenol behaves as an acompetitive activator of secreted urease with a Ka value of 0.7 mM. Evemia prunastri, atranorin, glycoprotein, secreted urease, lichen