To evaluate the clinical value of combined determination of serum PG I , PG II and GAS for early diagnosis of gastric cancer, the serum levels of PG I, PG II and GAS in 190 healthy controls and 129 patients with gastric disorders were measured by RIA. The 129 patients include 68 cases of gastric cancer. The results showed that the serum levels of PG I and PG I /PG II ratio in gastric cancer patients were obviously lower than those in healthy controls, while comparing with controls, the serum GAS levels were significantly higher. The diagnostic accuracy of the determinations for gastric cancer was evaluated by receiver operating characteristic (ROC) curve analysis. The area under the curve (AUC) levels of serum PG I, PG I /PG II ratio and GAS were 0.833, 0.842 and 0.851, respectively. As serum PG I or PG I /PG II ratio or GAS were combined, the sensitivity and specificity of determination for gastric cancer diagnosis were 94.2% and 73.4%, respectively. All these results indicated that the combined determination of serum PG I, PG II and GAS levels may be used as a tool for primary screening of gastric cancer.