Using a new microanalytical method authors investigated the AGP level in the sera of 41 healthy individuals and 87 patients with and without malignant diseases of gastrointestinal tract verified clinically by other diagnostic (image forming) techniques. It could be stated that serum AGP levels measured in healthy persons were in good agreement with the data of others, and selecting 80 mg/dl concentration as upper limit of normal values (cut-off level, mean + 2SD) the specificity of the test for a healthy population was 95 per cent. AGP content in the sera of patients with various malignancies of the gastrointestinal tract, mainly of colon and stomach was significantly higher in comparison to the healthy controls. On the other hand, 16 patients from 22 gastrointestinal cases without malignant diseases represented serum AGP concentrations within the normal range, while 6 patients with acute phase of inflammation had specifically elevated AGP levels. According to these data specificity of 72.7 per cent and sensitivity of 78.5 per cent (for colorectal tumours 82.9 per cent) of the test were obtained in average for the gastrointestinal malignancies. The positive predictive value of the marker was 89.5 per cent. Our investigations demonstrated that a marked elevation of serum AGP level indicates malignant process in the diseases of gastrointestinal tract with high probability. Results presented here led to the conclusion hat determination of the serum AGP concentration performed and evaluated simultaneously with other diagnostic (image forming) procedures can be applied successfully in the recognition of gastrointestinal tumours.