This study had three major goals: (1) to vigorously verify the presence of progesterone receptors in squamous cell carcinoma of the upper aerodigestive tract (HN-SCC). Antiprogesterone receptor monoclonal antibodies revealed a distinct band at approximately 120 kilodaltons in samples taken from two of four patients with HN-SCC. These results illustrate that progesterone receptor in HN-SCC has the same molecular weight as progesterone receptor in normal human uterus and human breast cancer. Steroid specificity and saturability results support the evidence that it is true progesterone receptors that are measured and not other receptors or sex steroid-binding globulins; (2) to confirm the biochemical function of progesterone receptors in HN-SCC by assessing the binding of progesterone receptor to acceptor sites on chromosomes in the nucleus; and (3) to establish the clinical significance of progesterone receptor measurement. Patients with positive assays were more likely to be free of disease a mean of 6 months after resection. We used logistic regression to account for site of primary disease, grade of tumor, and stage of disease. This logistic regression was significant with a p = 0.014. Patients with a binding index greater than 2 (19 of 73 patients) were 4.34 times more likely to be free of disease than patients with negative assays.