Anergy to 2,4-dinitrochlorobenzene (DNCB) has been reported as a highly significant adverse prognostic immunological factor in several studies of patients with squamous cell carcinomas involving the head and neck. Patients with these tumours often present with concurrent nutritional deficiencies. This paper reports the findings of a prospective study into both the nutritional status and general immune competence of 53 such patients.Analysis of the results has demonstrated a statistically highly significant positive correlation between nutritional status and both the delayed hypersensitivity response to DNCB, and the pretreatment total lymphocyte count levels. It is suggested that nutritional deficit may be a primary adverse prognostic factor in this disease group, with immunoincompetence a secondary phenomenon, and supporting evidence is presented. The consequent probable importance of nutritional status with regard to clinical trials, and the necessity for controlled studies to determine the possible beneficial effect of nutritional support on `cure' rates, are discussed.