The distribution of A, B, O(H) blood group antigens was studied in paraffin sections of 4 and 11 specimens, respectively, of normal skin and squamous cell carcinoma of the penis using specific red cell adherence (SRCA) test. In the normal skin of the penis the antigens appeared on the uppermost cornifying layers, while basal and malpighian layers were devoid of antigens. In squamous cell carcinoma of the penis the antigens were either absent or confined only to the epithelial pearl formations. Each of the 4 normal skins and 3 of the 11 carcinomas were antigen positive. As the blood group antigens were frequently absent in patients with carcinoma of the penis regardless of the tumor grade and stage as well as patient's condition, they lack the power to discriminate invasive potential.