In the present study an immunofluorescence using KH-2 cells as target cells, has been developed for the screening of 1200 serum samples from normal individuals and 450 of cases from patients with various malignancies. The positive anti-HTLV-I antibody rate in the former group is 0.083% (1/1200) and while in the latter it is found to be 1.8% (8/450) (including 3 adult T-cell leukemia/lymphoma cases of the 92 hematopoietic and 5 of 358 non-hematopoietic malignancies). The differences between the two groups are found to be significantly different (p value is less than 0.0001). In addition to the 3 adult T-cell leukemia/lymphoma cases, the 5 seropositive cancer patients are of 5 different diseases. We have searched for the adult T-cell leukemia virus antigen and the p19 core protein in lymphoid cells of seropositive persons and the only positive cases were from cells of two proven adult T-cell leukemia (ATL) patients. Our results suggest that Taiwan is not an endemic area of adult T-cell leukemia virus and that KH-2 cells may be used for the detection of anti-HTLV-I antibodies.