28 cases of carcinoma of the digestive tract were studied in order to assess the value of assaying a new tumour marker (CA 19-9) on monitoring the postoperative course of neoplasia. CEA, a tumour antigen of more certain dependability was assayed at the same time. In the case series examined it was found useful to monitor both antigens since although CA 19-9 is less sensitive then CEA in cancers of the large intestine, it is more sensitive in carcinomas of the stomach and pancreas. These early data will have to be confirmed on larger samples but in general terms they do indicate the value of the combined monitoring of this new antigen and CEA in the follow-up of patients given surgery for carcinoma of the digestive tract.