Carcinoembryonic antigen (CEA) concentrations were determined in the sera of 45 patients with a head and neck squamous cell carcinoma and of 13 controls. In 13 patients serial CEA measurements were made during the follow-up period. In 38% of the patients the serum CEA level was slightly elevated (greater than or equal to 2.5 ng/ml). Only 13% of the patients had clearly elevated CEA levels (greater than 5 ng/ml). CEA levels were significantly higher in patients with advanced, e.g. stage IV, disease but a correlation between serum CEA concentration and prognosis was not found. Patients who smoked had significantly higher serum CEA levels than non-smoking patients. In the serial determinations slight CEA elevations could be found in only 50% of patients with tumour recurrence. Combined with the data from the literature we conclude that serum CEA determination is not useful in predicting the outcome in patients with a head and neck squamous carcinoma.