Abstract: Objective To evaluate the diagnosis value of contents of serum and asocitic CA-50 in the cases with carcinomatous ascites. Methods The serum CA-50 content was measured by radioimmunoassay in 54 normal individuals,176 patients with carcinoma of digestive system and 160 patients with benign diseases. Results The normal value was 3.80+2.45Ku/L The content of serum CA-50 in patients with carcinoma were much higher than those of healthy people and patients with benign diseases(P＜0.001 in both),and this occurred in the early stage and became even more obverious in the late stage.Taking the normal mean value plus two times of standard deviation as positive,the positive rate was 85.8% for carcinoma of digestive system.There was only two positive in 52 normals with a fales positive rate of 3.7%. Conclusion The detection of both esrum CA-50 and ascitic CA-50 may have a certain clinical prectical value in carcinoma of the digestive system diognosis,differential diagnosis and the monitor, prediction of prognosis.