In order to establish Taiwan monkey lymphoblastoid cell lines, attempts were made to raise the susceptibility of monkey lymphocytes to Epstein-Barr virus (EBV) by chemical and enzymatic treatments. EBV infectivity to monkey T and B cells were tested by detection of EBV early antigens in infected cells with the indirect immunofluorescent antibody technique. Treatments of monkey unfractionated lymphocytes with DEAE-Dextran (160 microgram/ml) for 1 hr, ethylenediamine tetra-acetic acid (EDTA, 0.5%) for 10 min, 5-bromodeoxyuridine (BUdR, 12.5 microgram/ml) for 23 hr and 5-iodo-2'-deoxyuridine (IUdR, 12.5 microgram/ml) for 20 hr raised the susceptibility of the cells to EBV. However, trypsin treatment (0.05, 0.1 and 0.2%) at 37 degrees C for 5 min did not affect cell susceptibility to EBV. Unfractionated lymphocytes, T cells which were purified by rosette formation with sheep red blood cells, and a B cell-rich population obtained by the treatment of lymphocytes with antithymoycte serum were treated with the chemicals described above. The results showed that although the possibility of T cell susceptibility to EBV could not be ruled out because of 1 to 2.5% of B cell contamination in purified T cells, the main target cells in Taiwan monkey leukocytes for EBV infection were B cells.