Pleomorphic parotid gland adenomas (PPA's) have a variability of histopathologic appearances making it difficult to classify and its biological behavior is also difficult to predict. To find a better understanding of this phenomenon a retrospective causal study was undertaken on 25 benign and 17 malignant PPA's cases. Having exposed the underlying process it is hoped that it can be applied for the prediction of the malignant changes occur in PPA's depending on the expressions of oncogenes rasP-21, C-erbB-2 and P-53 immunohistochemically. The immunoexpression were defined by the criteria: 0=negative; +1=focal (<20%); +2=heterogenous (20-50%); and +3=diffuse (>50%). heterogenous and diffuse are considered to be an overexpression criterias. The immunoexpression percentage of ras P-21 (88.1%), C-erbB-2 (92.8%) and P-53 (97.6%) is highly significant (p<0.01) in emerging the variability of the biological behaviour of PPA's. The sensitivity of immunohistochemistry and Pvnegative (both 100%) are indicative of their abilities for detecting the malignant potentials of PPA's. The spesifisity of immunohistochemistry of 50% and the presence of false positive in the benign PPA's cases could be considered of having the potentials for malignant change. Apparently overexpression of the rasP-21, C-erbB-2 and P-53 plays a role as a dependable indicator of having the potentials of benign PPA's for malignant change.