Numbers and percentages of T and B cells in peripheral blood; blastogenic responses to PHA, Con A, and PWM; and serum levels of albumin, total protein, and IgA were assessed in patients with stages I to III operable squamous cell carcinoma of the upper aerodigestive passageways in the head and neck. The patients were categorized into two groups: those who remained tumor free and those in whom cancer recurred. It was found that pretreatment PHA- and Con A-induced blastogenesis was often depressed in patients in whom clinically apparent recurrences developed regardless of stage or nodal involvement. This point is consistent with the idea that cellular immune function (blastogenesis) can identify, within the clinical staging system (TN), subpopulations of patients who are less likely to survive after conventional therapy.