In combination with chemotherapy [ftorafur (FT)], allogeneic lymphoid cells were transferred to inhibit the growth of a 3-methylcholanthrene-induced transplantable KMT-17 fibrosarcoma in Wistar-King-Aptekman/Hok rats. The transference of allogeneic lymphoid cells 4 days after tumor inoculation did not prove effective in inhibiting the growth of the tumor; administration of FT (300 mg/kg) on Day 3 resulted in a 16.7% survival rate. However, a combination of the transfer of cells and administration of FT resulted in an improved effect of 55.0%. A low dose of FT (100 mg/kg) also increased the therapeutic effect in combination with allogeneic lymphoid cell transfer (28.0%). However, a high dose of FT (500 mg/kg) did not increase the therapeutic effect (30.0%), even if combined with allogeneic lymphoid cell transfer on Day 2, 4, 6, or 9, although a high dose of FT administered alone on Day 4 showed a direct antitumor effect (32.0%). This effect was rather diminished when the transfer was combined on Day 2. (7.1%). The differences in the combination effect of doses of FT seem to depend on the immune status of the host induced by treatment with FT. In order to investigate the mechanism of combination timing of FT and allogeneic lymphoid cell transfer, the specific delayed hypersensitivity reaction to KMT-17 tumor was assayed by the radioisotopic footpad method. The specific delayed hypersensitivity reaction was strengthened by an injection of FT (300 mg/kg).