In 42 control subjects and 134 patients with benign or malignant disease of the pancreas or large intestine, the recently produced tumour-associated antigen CA 12-5 was determined together with CEA and CA 19-9. Only 4% of controls and patients with benign disease (except those with acute pancreatitis) had CA 12-5 values above 35 U/ml, compared with 60% of patients with pancreas carcinoma and 21% with colon carcinoma. For the former (pancreas carcinoma) there was also a good correlation to stage of tumour (0 of 6 tumours stage TxN0M0, 7 of 11 TxN1M0, 16 of 20 TxN1M1 greater than 35 U/ml) and progression of the malignancy. Simultaneous determination of all three antigens increased the rate of tumour-marker positive patients from 87% (CA 19-9) to 92% for pancreas carcinoma and from 25% (CEA) to 51% for colon carcinoma.