The serum levels of Carcinoembryonic antigen, CA 19-9 and CA 50 were assessed in 60 patients with squamous cell carcinoma of the esophagus during the course of the disease. In 53 patients, the effect of preoperative or final treatment on tumor marker levels could be analysed, and the change in tumor marker levels discriminated significantly the patients who showed tumor mass/symptom regress from the patients who displayed progress or undecided change. Progress later in the course of the disease was reflected by a statistically significant increase in all three tumor marker assays, and in 8/18 (44%) patients the tumor marker increase was seen prior to other signs of tumor progression. The appearance of distant metastases was associated (11/12) with increase in CEA levels.