Esophageal carcinoma is the seventh most common cause of cancer-related death in the Western world. In Sweden, approximately 400 new esophageal carcinomas are diagnosed yearly. Cytokeratins (CK) are specific for epithelial cells and the expression profile usually remains unchanged even when the epithelium undergoes malignant transformation. In the present study, MonoTotal, a newly developed RIA-assay detecting circulating CK 8, 18 and 19 fragments, was investigated in sera from patients with esophageal carcinoma. Serum samples from 40 patients with esophageal carcinoma were collected. The median value of circulating CK 8, 18 and 19 measured with MonoTotal was 378 U/L (range 53-6843) and with regard to the defined cut-off (< 75 U/L), 39/40 (98%) patients were shown to have elevated levels of circulating CK 8, 18 and 19. Patients with localized disease had a median value of circulating CK 8, 18 and 19 of 305 U/L (mean: 500 U/L), whereas the corresponding value for metastatic disease was 771 U/L (mean: 1506 U/L). This difference was statistically significant (P = 0.016). Circulating CK 8, 18 and 19, according to cut-off, were not associated with survival in univariate analysis (P = 0.34). However, continuous values of circulating levels of CK 8, 18 and 19 were associated with survival (P = 0.000083) in univariate as well as in the multivariate analysis (P = 0.03). In conclusion, circulating CK 8, 18 and 19 correlates with increased tumor burden and might, in conjunction with other clinical parameters, aid the clinician in estimating the prognosis of the individual patient.