The immunotoxic responses of allogeneic B6C3F1-mice and syngeneic CD2F1-mice bearing L1210 mouse leukemia to ethylene-glycol- monomethyl-ether (109864) (EGME) and ethylene-glycol-monoethyl-ether (110805) (EGEE) were investigated. B6C3F1-mice received oral doses of 600, 1,200 or 2,400 milligrams per kilogram (mg/kg) EGEE, or 300, 600, or 1,200mg/kg EGME 12 to 8 days prior to tumor transplantation, or cyclophosphamide (50180) (CP) at 180mg/kg intraperitoneally 1 day prior to tumor transplant. On day of tumor transplant (day 0) the mice were challenged with 100, 1,000, 100,000, or 3,000,000 L1210 cells intraperitoneally. Syngeneic mice were challenged with 100,000 L1210 cells on day 0 and were treated on days 1 to 5 and 8 to 12 at the same EGEE and EGME doses as the allogeneic mice. Negative controls for each strain were given distilled water on days corresponding to the chemical treatment days. Blood smears of allogeneic mice were made for differential counts on the last day of treatment, day of death, and 43 days post tumor transplantation. The median survival time for the controls was 8 days. EGME and EGEE treatment did not affect median survival time in syngeneic mice, indicating that these compounds did not inhibit tumor growth. All allogeneic mice challenged with 3,000,000 L1210 cells and receiving water or CP treatment died. But mice receiving EGME or EGEE and challenged with the same tumor cell concentration showed over 83 percent survival rates. Differential counts showed presence of monocytosis in mice dying before day 43 post tumor transplantation. Autopsies of allogeneic survivors on day 43 revealed cholecystitis. The authors conclude that EGEE and EGME exert their anti tumor effect through increased immunological competence or immunomodulation.