The ras P²¹ expression in non-cancer lesion and carcinomas of the stomach was quantitativaly studied by flow cytometry,and relation of ras P²¹ expression to DNA ploid and cellular proliferation index were inquired.The results showed that ras P²¹ expression was higher in carcinomas than in non-cancer lesion one’s of thee stomach.In non-cancer lesions,ras P²¹ expression in precancer lesion was higher than in chronic atrophic gastritis,and the raiser of fluorescence index in ras P²¹ expression was found with raiser of histological grade. DNA ploid was associated with ras P²¹ expression.