A 23-year-old woman, diagnosed with a synovial sarcoma of the peritoneum, underwent an operation for tumor extraction. In the postoperative period, Ukrain was injected i.v. at a dose of 10 mg on alternate days, for a total of 10 injections. After a 2-month break, this schedule was repeated. Ukrain treatment was well tolerated by the patient and there were no complications in the postoperative period. The following changes in immunohematological parameters were observed: increased total leucocytes, T lymphocytes and T helpers. Nearly 4 years after Ukrain therapy, the patient is in complete remission.