Using the C.B.17 scid mouse strain, we have developed a model of disseminated leukaemia and myeloma using five human cell lines, CCRF-Cem, Molt-4, Raji, IM9 and HS-Sultan. Introduction of any of these cell lines by either an intravenous or an intraperitoneal route eventually kills the mouse due to leukaemia or myeloma cell load. Neoplastic cells can be found in the blood, liver and bone marrow. Intraperitoneal transfer produces a local solid tumour whereas intravenous transfer produces foci of neoplastic cells in the spine and brain. A single dose of melphalan is able to increase survival time from infection of a lethal dose of the T-cell leukaemia cell line, CCRF-Cem.