Anticancer therapeutic potential and immune response modifying activity of recombinant human interferon gamma (Lucky Central Laboratory, Korea) were evaluated in advanced colorectal carcinoma patients. 31 patients were randomized to two groups: A group receiving 5 x 10 units I'M daily for 1 weeks and B group given 10x10' units IM daily for 4 weeks. 27 patients were evaluable for toxicities. Reversible toxicities of WHO grade <3 were noted in both groups which included fever, malaise, anorexia, and headar.he in order of decreasing freque.ncy. Dose dependent toxicities uere obvious since group B showed more frequent and severe toxicities. Among the laboratory changes, leukopenia was most frequent with 6 out of IS group B patients. While receiving IFN-gamma, NK activity and THI+) lymphocytes uere increased in the peripheral blood mononuclear cells. But Tacl+) lymphocytes were not increased in proportion. These immunoiogic changes were about same in both groups. 24 patients were evaluable for response with no antitumur responses observed. Only 3 patients showed stable disease for mean duration of 3 months. Our results suggest that 5 x 10 units of IFN-gamma injcction daily is tolerable and sufficient for enhancing host immune response against cancer, although inact.ive in the real eradication of advanced colorectal cancer. Additional clinical investigations are warranted in terms of combination with interferons and other biological response modifiers.