A series of derivatives belonging to a new class of compounds (R4-todit) were highly cytotoxic to a panel of leukaemia- and solid tumour-derived cell lines (IC50 = 0.06-20 microM). The most potent compound was the butyl4 derivative (IC50 = 0.06-5.1 microM); T leukaemia and melanoma cells were the most susceptible cells to this inhibitor (IC50 0.06 microM and 0.1 microM, respectively). The effect of butyl4-todit was irreversible, and led to progressive cell death. The compound showed a comparable potency against exponentially growing and stationary phase cells, and against cell lines expressing the MDR phenotype. The cytotoxicity of butyl4-todit in human normal PBL was up to 20 fold lower than that shown against T leukaemia cells. When tested for antiangiogenic activity in vivo, 1.5 mg/Kg butyl4-todit resulted in over 70% inhibition of the angiogenesis process induced in mice by Kaposi's sarcoma cell secreted products.