The oncogene ras P21 and P53 gene protein expression in the benign and malignant pleomorphic adenomas of salivary gland were quantitatively studied by flow cytometry and cellular immunofluorescence staining technique. The results showed that the ras P21 expression was found in 78% and 100% of the benign and malignant pleomorphic adenoma, respectively. The P53 protein was detected in 81% and 100% of the benign and malignant pleomorphic adenoma, respectively. The ras P21 and P53 protein were negative in the normal parotid tissue. The obvious different statistical significances of the fluorescence indexes (FI) in ras P21 and P53 expression were found between the benign and malignant pleomorphic adenoma (P < 0.001, respectively) as well as between the normal parotid tissue and the benign pleomorphic adenoma (P < 0.001, respectively). These results indicate that activation of ras oncogene and the mutation of P53 gene may play important roles in the tumourigenesis and the malignant transformation of the pleomorphic adenoma.