Tumor markers such as carcinoembryonic antigen (CEA) and CA19-9 were analyzed as response indicators and prognostic factors in advanced colorectal carcinoma. Eighty-five patients participated in a phase II chemotherapy study from October 1984 to July 1990. A three-drug schedule was administered including low dose epirubicin and sequential methotrexate 5-fluorouracil, followed by leucovorin rescue. Serum specimens for CEA and CA19-9 were obtained prior to the initiation of chemotherapy, and subsequently at 4-6 weeks' intervals. In univariate analysis Karnofsky, the site of the primary tumor, the extent of metastases, the presence of abdominal or liver metastases, serum CEA (cut-off of 20 micrograms/l), and CA19-9 levels correlated with survival. In stepwise multivariate analysis an elevated CA19-9 level, a poor Karnofsky, and the presence of liver metastases were independent adverse prognostic factors. Tumors originating from the left colon had a better prognosis than the others. This was related to a higher response rate in this patient group. Serum CA19-9 level was the most significant prognostic factor whether it was entered as a continuous or as a dichotomized variable into the model. The median survival of patients with a normal CA19-9 level was 30.0 months (lower 95% confidence interval: 16.4 months; upper limit was not calculable), and with an elevated CA19-9 value 10.3 months (8.0-12.6 months, 95% confidence interval). Five of 85 patients had a complete response and 20 a partial response, the overall response rate being 29%. When compared with tumor shrinkage, "CEA response" and "CA19-9 response" had a sensitivity of 84% and 88% and specificity of 77% and 67%, respectively. In conclusion, serum CEA value seems to be the best tumor marker for response prediction, while CA19-9 level is one of the best available prognostic indicators in advanced colorectal carcinoma.