Histologic sections of seven squamous cell carcinomas (SCC), 13 basal cell carcinomas (BCC), and a Bowenoid actinic keratoses were examined for expression of HLA class 1 antigens (HLA-ABC) using a monoclonal antibody and an immunoperoxidase technique. Expression of beta 2-microglobulin was examined with a polyclonal antibody method. Neither cell marker was detected within the Bowenoid actinic keratoses. Squamous cell carcinomas and basal cell carcinomas exhibited decreased expression of both HLA-ABC and beta 2-microglobulin and often did not express these antigens at all. HLA-ABC was present in only two of 13 basal cell carcinomas and four of seven squamous cell carcinomas. beta 2-microglobulin was present in one of 13 basal cell carcinomas and two of seven squamous cell carcinomas. When present, these antigens often were present in a few areas of the tumor, but absent in others. In both SCC and BCC, both antigens were usually lost simultaneously. In all tumors with beta 2-microglobulin, HLA-ABC also was retained. There was no apparent relationship of anatomic site or type of tumor with retention of surface antigens. Since some tumors or portions of tumors retained HLA-ABC and beta 2-microglobulin on their surfaces, the absence of these antigens is not an absolute marker for malignancy.