Antisera were prepared in rabbits against urea-extractable proteins of normal mouse epidermis, papillomas, and squamous-cell carcinomas. The relationship of these antisera and the antigens of the three tissues was studied by immunodiffusion in agar before and after inhibition treatment of these antisera with the three antigens. These procedures revealed that (1) the epidermis has urea-extractable antigens which are present in much smaller amounts in the urea extracts of papillomas and squamous-cell carcinomas, and (2) papillomas and carcinomas have several urea-extractable antigens in common, and both the benign and malignant growths each have at least one antigen present in greater amount in one tissue than in the other. The papilloma and carcinoma antigens are present, but in small amounts in normal epidermis.