The phosphamidase content in normal and pathologic tissues of 37 biopsies from the oral cavity was examined using the histochemical method of Gomori. High concentrations of phosphamidase were found in the epithelia of epidermoid carcinoma, leukoplakia, papilloma, pleomorphic salivary gland tumor, in the proliferating connective tissue of a giant cell tumor and in the epithelium adjacent to a fibroma and in the epithelium of blastomycosis. Low concentrations of phosphamidase were found in a few cases of inflammation of the mucous membrane associated with hyperkeratosis. The phosphamidase reaction was negative for normal epithelium and connective tissue of the oral mucous membrane, the lining of the maxillary sinus and mucous glands. The present limitations of the technique are discussed and some precautions against erroneous conclusions presented.