The serum SCC antigen levels of patients with head and neck tumours are being studied in a prospective study to evaluate their clinical relevance. Concentrations above 2 ng/ml are considered to be abnormal. Preliminary results of the study after a 12-month period including 167 patients are reported: In only 28% of the patients with actual carcinoma of the head and neck the serum levels were pathological (Fig. 6), most commonly in oropharyngeal tumours (nearly 50%). The incidence of abnormal SCC-antigen concentration only rarely increased with increasing tumour extension (Fig. 7), but to a considerably greater extent in well-differentiated than in poorly or non-differentiated squamous cell carcinomas (Fig. 8). Tendencies, but no statistically significant correlation, were found between the Karnofsky index and the serum levels (Fig. 9) - as well as between the time of remission after successful tumour treatment and decreasing serum concentrations (Fig. 10). At the time of recurrence of the tumour, SCC-antigen serum levels had not been able to predict the clinical recurrence (Fig. 11). Since the assessment of SCC-antigen concentration is neither highly specific nor sensitive, the usefulness of this tumour marker test must be--at least according to the present state of the art--regarded as rather low.