Serum copper and ceruloplasmin levels (SCL, SCeL) in 57 patients with advanced cancer of the stomach (35 cases) or large intestine (22 cases) treated with polychemotherapy were studies. In gastroenteric cancer, SCL, which are already high in untreated patients, have a tendency to increase further in cases of progression of the disease, while they seem to significantly decrease in cases of remission. SCeL during the trial appeared to be correlated to the clinical evolution of the disease only in the case of stomach cancer. In large intestine cancer, SCeL did not show any significant variation in relation to the normal range. These observations, in particular on the behavior of SCL in the neoplasms of the digestive tract, are in accordance with the results of other studies. The authors are inclined to attach a diagnostic and prognostic value to the variation in SCL and SCeL in gastrointestinal cancer.