OBJECTIVE To investigate the correlation between the expression of key proto-oncogenes playing major roles in tumorigenic process and abnormal sarring. METHODS Immunohistochemical technique was performed to detect the expressions of c-myc, c-fos and ras p21 proteins on hypertrophic scars, keloids and normal skin. Image analysis was used to compare their quantitative difference of expression. RESULTS C-myc and c-fos expressions on the nucleus of fibroblasts of hypertrophic and keloid scars were significantly higher than normal skin controls, and there was no difference between the two lesions. Ras p21 expression was not detected on the fibroblasts of hypertrophic and keloid scars. CONCLUSIONS 1. c-myc and c-fos oncogenes are activated on hypertrophic and keloid scars, which may contribute to proliferation and differentiation of fibroblasts, synthesis and degradation of collagen and regulation of cytokines and induce abnormal scarring, the mechanisms of their effects remain to be further studied. 2. Ras gene may not mutate or its mutations may not play a major role in the process of abnormal scarring. 3. Only part of proto-oncogenes moderately expressed on abnormal scars. The expression of multiple oncogenes does not coexist in abnormal scars may be the cause of their less chances to induce malignant transformation.