Summary Inhibition of angiogenesis through blocking of growth factors involved in this process could be a novel therapeutic approach in several important pathologies, neoplasia among them. Suramin has recently been described to possess antineoplastic activity in animals and humans, and it has been proposed that an important role in this activity is played by antagonism of growth factors and especially bFGF. To investigate this hypothesis in vivo, we used gelatin sponges loaded with bFGF and implanted subcutaneously in mice. Suramin showed an inhibitory activity on bFGF-induced angiogenesis, whereas it was inactive in the case of heparin-complexed bFGF. Suramin was also studied in an in vivo model of tumour-induced angiogenesis using the murine M5076 reticulosarcoma, a tumour producing significant levels of bFGF. Suramin was able to reduce tumour growth and tumour induced angiogenesis, and exogenous administration of bFGF countered suramin effects.Physiologically, angiogenesis (i.e. the formation of new capillary vessels), is an important event in embryonic development and in the adult female reproductive cycle (Gospodarowicz & Thakral, 1978). Under pathological conditions neovascularisation occurs during the wound healing process (Knighton, 1981) and in a variety of diseases ranging from diabetic retinopathy to psoriasis and several types of chronic inflammations (Goldie, 1969). It has also been shown that the process of solid tumours growth is angiogenesisdependent (Gullino, 1978;Folkman, 1990). Several substances of different chemical nature and cellular origin, including growth factors produced by the neoplastic cells themselves, have been described to be involved in tumourinduced neoangiogenesis (Shing et al., 1985;Folkman & Klagsbrun, 1987) by directly and/or indirectly stimulating endothelial cells proliferation and/or migration (Ausprunk & Folkman, 1977). One of the better characterised among such angiogenic factors is basic Fibroblast Growth Factor (bFGF) (Rifkin & Moscatelli, 1989), whose presence in a large number of normal and malignant cells is well established, and that has been implicated as a major contributing factor in both physiological and pathological neovessel formation (Folkman et al., 1988;Klagsbrun et al., 1986;Thompson et al., 1988;Hayek et al., 1987). Since solid tumour growth and progression are strictly dependent from neovessel formation (Folkman et al., 1989;Brem et al., 1977) interfering with this process by counteracting the effect of angiogenic growth factors could represent a novel and selective therapeutic approach to malignancy.Suramin, a polysulphonated trypan red derivative used in the past as antitrypanosomic agent (Hawking et al., 1987), has recently generated interest as an antinoplastic agent (Stein et al., 1989;Myers et al., 1990; Richard, 1990;Hosang, 1985;Mills et al., 1990) to their cell surface receptors through direct complexation of the growth factors and/or via a modification of the cell receptor (Coffey et al., 1987). This activity could explain suramin inhibitio...