Abstract: AT-16, a new chemical compound synthesized at our Institute, is a derivative of nitrogen mustard containing the main skeleton of chloramphenicol. Its chemical structure is It was demonstrated that AT-16 had a marked therapeutic effect against several experimental tumors and a low toxicity in animals. 1.AT-16, given orally at 50—300mg/kg/day for 7 days, exhibited a marked inhibitory action on sarcoma M-57 and Jensen sarcoma in rats and sarcoma 180, brain tumor 53 and the solid tumor of lymphatic leukemia in mice. In rats bearing sarcoma M-57 after two weeks of inoculation, AT-16 also exerted a marked tumor-inhibiting effect. The tumor mass was markedly reduced and could be brought into complete regression. 2. AT-16, 200mg/kg/day, could prolong the survival period of rats bearing Yoshida ascites sarcoma by about 6 folds. 3. In mice and rats after single intragastric administration of AT-16, the acute oral LD₅₀ was found to be above 4000 mg/kg; the subacute LD₅₀ of AT-16 was 690mg/kg for mice and 526 mg/kg for rats. 4. AT-16 was introduced to rabbits by stomach tube at the dosages of 50, 100, 200 or 300mg/kg/day for 10 days. The blood cell counts, body weight, urine and stool routine examinations were carried out before and after the administration of the drug. No toxic effects were found at the dosage of 50 mg/kg. When the dosage was increased to 100—200mg/kg, a temporary decrease in w.b.c, was noted in some animals. At 300 mg/kg the w.b.c, decreased more markedly and the body weight was also reduced. At the end of administration, 1 or 2 animals of each group were sacrificed and pathological examinations were carried out. It was found that at the higher dosage the animals showed urinary retention and tympanites. No significant abnormalities were observed in other visceral organs on macroscopic examinations, but under the microscope, cloudy swelling was found to be present in the heart, liver, and kidneys. 5. Six monkeys were divided into three groups and the drug was given orally at the dosages of 10, 30 and 50 mg/kg for 14 days. The respiration, heart-rate, EKG, blood pressure, blood cell counts, stool routine, and body weight were examined. At the dosage of 50 mg/kg a diminution in w.b.c, was observed by the end of the treatment, but recovery after Cessation of the drug was rapid. No significant change was found in other examinations. AT-16 has been sent for clinical trials and the results will be published elsewhere.