The serum levels of squamous cell carcinoma (SCC) associated antigen are related to the course of the therapy in 91 cases of advanced head and neck cancers. Without statistical significance the findings may lead to the following statements: 1. Serum levels below 2 ng/ml before treatment are not related to tumour growth. 2. Serum levels above 2 ng/ml before treatment are likely to be regarded as tumour-associated. 3. High and low level curves of not operated patients show a quantitatively different reaction to the course of a combined simultaneous radiochemotherapy. 4. Initially increasing serum levels under combined therapy may be interpreted as related to cell death or result of a production or proliferation stimulus. 5. High serum levels and low serum levels in tumour patients might be regarded as an expression of different biological activities in the tumour. 6. The comparison of the survival rates of high level tumours to low level tumours raises the question as to whether this different biological activity might be related to clinical malignancy.