Dinitrochlorobenzene (2-4 DNCB) forms a hapten with skin protein when topically applied. The delayed hypersensitivity reaction which secondary application produces is useful to measure cell-mediated immunity as a gross measure of cancer immunity. Lymphocytopenia and anergy to attempted delayed hypersensitivity elicitation may both reflect poor host response to neoplasia. A prospective study on 55 patients with localized or regional squamous cell carcinoma of the larynx, pharynx and mouth was done. These patients were sensitized and stimulated with DNCB and lymphocyte counts measured. Eighty-eight percent of positive DNCB reactors were alive and tumor free at one year while 53 percent of non-responders survived free of disease. All 19 DNCB responders with normal or increased lymphocyte counts survived without recurrence. The potential usefulness of prognostic evaluation of host response is described.