Previous studies showed that a cartilage-derived anti-tumor factor (CATF), which was extracted from bovine cartilage with 1 M guanidine hydrochloride, inhibited the growth of solid sarcoma 180, but not the growth of ascites tumors of sarcoma 180 [Suzuki, F. et al. Jpn. J. Bone Metab., 2, 231-235 (1984)]. This study showed that CATF inhibited the proliferation and DNA synthesis of endothelial cells isolated from bovine pulmonary artery, but not the proliferations of sarcoma 180, L1210 and L cells. These results suggest that CATF has anti-angiogenic properties, thereby inhibiting the growth of solid tumors.