The murine monoclonal antibody (A9), raised to the human squamous cell carcinoma (SCC) cell-line UM-SCC-1, defines a squamous cell antigen associated with aggressive biologic behavior of SCC cell lines in vivo and in vitro. In the present investigation, A9 antigen was detected in tissue sections from 37 consecutive, previously untreated patients with SCC of the head and neck. All tumors were positive for A9 binding, although three distinct patterns (reflecting different intensities of A9 expression) were identified. The intensity of A9 expression was independent of primary tumor site, tumor differentiation, keratinization, or growth pattern. The frequency of high expression (Pattern 1) grew with increasing T class, N class, and tumor stage, and was associated with loss of blood group expression in the tumor and with low levels of lymphocyte infiltration in the tumor. Strong A9 expression had a statistically significant association with low nuclear grade (i.e., tumors with more mature and fewer enlarged nuclei, P = 0.019), low vascular/stromal response (i.e., patchy response rather than continuous, P = 0.014), and impaired in vitro lymphokine production by peripheral blood leukocytes (P = 0.0011). Of greatest interest, however, was the strong association of high A9 expression with shortened disease-free interval (DFI) (P = 0.085) and survival (P = 0.081) relative to patients with weak A9 tumor staining (Patterns 2 and 3). Similarly, the loss of blood group antigen expression was strongly associated with decreased DFI (P = 0.038) and survival (P = 0.062). While neither Pattern 1 A9 expression nor loss of blood group reach statistical significance in prediction of survival, the combination of Pattern 1 A9 expression and loss of blood group expression in primary tumors was significantly associated, both with decreased disease-free interval (P = 0.017) and with decreased overall survival (P = 0.011) (median length of follow-up = 22 months). The length of follow-up (LFU) ranged from 2 to 38 months, with a median LFU of 22 months. While the number of patients (37) is small, the significant association between the expression of these cell-surface markers with relapse and survival indicates that immunohistologic staining of the primary tumor will be an important prognostic indicator useful in identification of individual patients at greatest risk of recurrence or early death from head and neck cancer, independent of tumor size, site, or stage at presentation. These markers may thus provide means of selecting patients who should receive adjuvant therapy and more intensive monitoring for the early detection of recurrent disease.