The tyrosinase isoenzyme patterns of six species of agaric Basidiomycetes were examined by acrylamide gel electrophoresis, Immunoelectrophoresis, immunodiffusion in agar, and hydroxylapatite column chromatography. Acrylamide gel electrophoresis produced the best separation of isoenzymes and other proteins. All six species demonstrated a multiplicity of isoenzymes ranging from seven major forms in Coprinus micaceus to 10 in Agaricus hortensis. Preliminary data indicate that a natural inhibitor of tyrosinase activity is present in all the species examined except in Coprinus comatus.