Abstract: The results of the detection and identification of antibodies to extractable nuclear antigens(ENA) by the use of passive hemagglutination(PHA) and counterimmunoelectrophoresis(CIE) test concomitantly are analysed and compared in this article.It was found that 60 of 168 samples of sera (35.7%)from patients with SLE showed antibody to ribonucleopr tein(RNP) component of ENA, and 67(39.9%) had antibody to the Sm antigen. All sera from 15 patients with MCTD(100%) had antibody to the RNP.PHA was more sensitive for detection of anti-Sm,while CIE detected more anti-RNP.Heating of ENA at 56℃ for 1 hour has the same effect as the use of ribonuclease in the differentiation of RNP and Sm antibodies in PHA test.