The role of angiogenesis in solid tumours is well recognised, but its importance in haematological malignancies is less well understood. In leukaemia, mainly the determination of microvascular density utilising immunohistochemistry in the bone marrow trephines and the measurement of soluble angiogenic factors have led to the recognition that angiogenesis may be important in leukaemia as well. In this study, the soluble form of the endothelial cell activation/proliferation (i.e., angiogenesis) marker CD105 and its ligands TGFbeta-1 and -3, as well as the ligand/receptor complexes in plasma from children with acute lymphoblastic leukaemia (ALL) were quantified. The plasma level of CD105 was significantly higher in patients with common ALL compared to controls, while the TGFbeta-3 level was lower in patients. Neither the CD105 or TGFbeta-3 levels were of prognostic value, nor did they correlate with any of the known prognostic indicators, such as white blood cell counts. There were no significant differences between the plasma levels of any of the other parameters, such as TGFbeta-1 or the ligand receptor complexes, in children with leukaemia compared to controls. Our results support the role of angiogenesis in leukaemia and suggest that anti-angiogenesis may be a therapeutic target in leukaemia.