HLA class I and class II antigen expression on squamous cell carcinoma of the head and neck. We compared human major histocompatibility (HLA) class I and class II antigen expression on squamous cell carcinoma of the head and neck with that on normal mucosa. Frozen sections of a consecutive series of 30 squamous cell carcinomas were stained with the monoclonal antibodies W6/32 (class I) and anti-DR (class II) using an immunoperoxidase technique. Normal mucosa showed class I and class II expression in the basal layers only. Class I expression on tumors was diffuse in 87%, patchy in 10%, and scattered in 3%. Class II expression on tumors was diffuse in 20%, patchy in 53%, scattered in 20%, and absent in 7%. Patterns of expression did not correlate significantly with clinical parameters, including survival, except that class II diffuse and patchy patterns were found to correlate with more poorly differentiated tumors. 