The aim of this study was to measure the serum level of the tumour markers CA 195 and CEA in patients with either colorectal or pancreatic cancer both before and at serial intervals after operation. CA 195 and CEA were measured in 199 patients with colorectal cancer and 52 patients with pancreatic cancer. The median concentrations of CA 195 were 3.0 u/ml (interquartile range 3.0-4.5 u/ml) in patients with a Dukes' stage A lesion, 5.8 u/ml (3.0-18.2 u/ml) in patients with a Dukes' stage B lesion, 6.1 u/ml (3.0-24.7 u/ml) in patients with a Dukes' stage C and 23.8 u/ml (11.1-409.0 u/ml) in patients with metastatic disease (normal range 0-7 u/ml). The median levels of CEA were 2.6 ng/ml (1.7-3.3 ng/ml) for Dukes' stage A, 3.3 ng/ml (1.7-7.2 ng/ml) for Dukes' stage B, 3.7 ng/ml (2.2-7.9 ng/ml) for Dukes' stage C and 34.5 ng/ml (13.3-289.4 ng/ml) for metastatic disease. A rising level of CA 195 or CEA after operation suggested recurrence of the tumour. In none of these patients was the recurrence operable. In patients with pancreatic adenocarcinoma, the level of CA 195 was significantly higher in patients with metastatic disease but it did not discriminate between resectable and unresectable disease. The duration of survival correlated with the initial level of CA 195 (Rs = -0.66, p less than 0.001).