Abstract: CD44, the receptor for hyaluronic acid, has complex functions in cellular physiology, cell migration and tumour metastasis. The inventors have previously found that human CD44 receptor overexpression in mouse fibrosarcoma cells inhibits subcutaneous tumour growth in mice [Kogerman et al., Oncogene 1997; 15:1407-16; Kogerman et al., Clin Exp Metastasis 1998; 16:83-93]. Here it is demonstrated that a tumour growth inhibitory effect of CD44 is caused by block of angiogenesis. Furthermore, the inventors have found that soluble recombinant CD44 hyaluronic acid binding domain (CD44HABD) inhibits angiogenesis in vivo in cLick and mouse and thereby inhibits human tumour growth of various origins. The anti-angiogenic effect of CD44-HABD is independent of hyaluronic acid (HA) binding, since non-HA-binding mutants of CD44HABD still maintain anti-angiogenic properties.