Objective To study serum p53 protein as a predictive for unfavorable responseto transarterial oily chemoembolization (TOCE) in patients with hepatocellularcarcinoma. Methods The populations consisted of new cases of hepatocellular carcinoma whowere treated with transarterial oily chemoembolization at Radiology InterventionUnit. Department of Radiology, King Chulalongkorn Memorial Hospital during the 1('th)January 1999 and the 31('th) December 1999. With the expectation that the test would havesensitivity of at least 90 % and on least than 15 % error, the sample size was 38.Serum was kept prior the chemoembolization. Serum p53 protein was blindly measured byELISA method in picogram per milliliter. Data was analysed by statistical methodologyto calculate sensitivity, specificity. positive and negative predictive values. Results: There were 45 hepatocellular carcinoma patients enrolled into thisstudy. Thirty-two were male and thirteen were female. Male per female ratio was 2.45:1 The median of age was 59 years and mean of age was 56.42 years.(Range 31-74 years).Risk factors consisted of hepatitis B virus in 24 cases (53.3%), hepatitis C 6 cases(13.3%) and history of alcoholic consumption 12 cases (26.7%). Twenty-eight cases(62.2%) were associated with cirrhosis. TNM stagings were stage II 4.4%, stage IIIA42.2 %, and stage IVA 53.3%. Okuda stagings were stage I 140%, stage II 55.6%. andstage III 4.4%. Median serum alpha-fetoprotein level was 351.95 lU/ml. (range1.6-400000 lU/ml). Forty-one of prechemoembolization p53 serum were kept and serump53 protein was detected in 10 cases (24.4%). The ranges of p53 protein were 5-1147pg/ml. Forty-one cases were evaluable for tumor response to TOCE and achieved apartial response of 41.46%. Thirty-seven patients had information both serum p53 andthe response of the treatment. Patients who had a positive p53 test had a responserate only 33.3% whereas the patients with negative p53 test had a response rate of50%. How ever. the p-value was 0.462 by Fisher's exact test. The serum p53 proteintest has sensitivity of 30.0%, specificity of 82.3%, positive predictive value of66.7 % and negative predictive value 50%. Conclusions 1. The serum p53 protein by ELISA test to determine the response ofchemoembolization has 30.0 % of sensitivity, 82.3 % of specificity. 66.7 % ofpositive predictive value and 50 % negative predictive value. 2. Serum p53 protein, which is measured by ELISA. cannot be used as apredictive factor for unfavorable response to transarterial oily chemoembolization.However, there is a trend of lower response rate to chemoembolization if the serump53 test is positive.