The presence of anti-nuclear antibodies (ANA) has been studied in 433 sera from 305 patients with anaplastic nasopharyngeal carcinoma (NPC) in Taiwan, by means of indirect fluorescent antibody method. Another 134 sera from normal adults or from patients with other diseases served as controls. Patients with NPC showed positive rate of 23.1%. Forty-two patients with other malignant and 25 patients with benign tumors of the head and neck showed positive rates of 9.5% and 8.0%, respectively. Forty-eight patients with inflammatory diseases and 19 normal adults were negative. The presence of ANA in 103 NPC patients before treatment was analyzed in detail. The positive rate was not significantly influenced by the age and sex of the patients, by the duration of the disease, by the extent of primary tumor and the presence of neck metastasis. But the positive rate rose as the anti-EB-VCA titer increased. This positive correlation of ANA and anti-EB-VCA antibodies was also significant in all the NPC sera. During and at the end of irradiation therapy, the ANA positive rates showed no remarkable variation. After treatment of the disease, ANA positive rate decreased gradually and this reduction became apparent after three years of remission of the disease. But the presence of ANA in NPC patients was not related to the prognosis of the patients. The possible mechanism in production of ANA in NPC patients was discussed with special reference to EB virus.