Serum levels of several tumor markers were studied in 96 patients with untreated primary squamous cell carcinoma of the esophagus. Three markers specific for digestive tract malignancies--CEA, CA19.9 and CA50--and two non organ specific indicators of malignancy--ferritin and TPA--were evaluated. Positivity rates of CA19.9 and CA50 were very low (4.4% and 8.6% respectively); the markers were therefore considered ineffective in the disease. CEA, TPA and ferritin showed a fair positivity rate (27.1%, 28.1%, 33.7% respectively); CEA and TPA were directly related to clinical stage, CEA levels being significantly higher in stage IV than in stage III cases (p = 0.016). TPA preoperatory levels were also directly related to a lower survival probability (p = 0.004). CEA showed significantly lower levels in tumors of lower than in those of middle (p = 0.03) and upper esophagus (p = 0.004). TPA showed a similar behaviour with lower levels in tumors of lower than of middle esophagus (p = 0.03). These findings could be due to a bulky metabolism of tumor markers drained via portail vein in the liver. From our data the following conclusions may be drawn: 1) CEA and TPA may be useful in the staging of esophageal cancer as an ancillary tool to assess the extent of the disease; 2) tumor location is an important variable when evaluating blood levels of tumor markers in patients with esophageal cancer.