The effects of human interferon-beta (IFN-beta, MR-21) on the growth of xenografted human tumors in nude mice were examined. IFN-beta was administered to mice with malignant melanoma (SK-MEL-28 and Sk-14) intratumorally at a dose of 1 X 10(5)-3 X 10(5) IU/mouse, with acute leukemia (CCRF-HSB-2) intratumorally at a dose of 3 X 10(5) IU/mouse, with glioblastoma (U-373 MG) intravenously or intratumorally at a dose of 1 X 10(5)-6 X 10(5) IU/mouse, or with uterine cervical tumor (HeLa S3) intravenously at a dose of 0.3 X 10(5)-1 X 10(5) IU/mouse. IFN-beta inhibited the growth of all of these tumors in a dose-dependent manner.