Abstract: In this paper, Sm and RNP activities of the ENA extracted from pig thymus are investigated. Using counterimmunoelectrophoresis (CIE), when the pig thymus ENA were used as antigens, the positivities of anti-Sm and anti-RNP antibodies in the sera of the patients with connective tissue diseases (including SLE etc.) were comparable to the ENA extracted from rabbit thymus acetone powder. It was confirmed that the antibodies were anti-Sm and anti-RNP by reference CIE and agarose double immunodiffusion assay.