During our efforts to develop monoclonal antibodies (MAbs) to tumor associated surface antigens of squamous cell carcinomas of the head and neck, monoclonal antibody K 931 was produced. The high affinity antibody (K(a) 5.0 x 1010 M-1) showed reactivity with 58 out of 62 squamous carcinomas of the head and neck. In contrast normal squamous epithelium as found in epidermis, oral cavity, epiglottis, pharynx, larynx and esophagus did not express the antigen. All other tested epithelial (simple and transitional) tissues did express the antigen, but non-epithelial tissues were negative. Further characterization revealed that the antigen represents the 17-1A antigen. A not earlier reported, enhanced expression of the 17-1A antigen was observed among some primary and all metastatic SCC.