The present invention relates to the field of pathological angiogenesis and arteriogenesis and, in particular, to a stress-induced phenotype in a transgenic mouse (PIGF.sup.-/-) that does not produce Placental Growth Factor (PIGF) and that demonstrates an impaired vascular endothelial growth factor (VEGF)-dependent response. PIGF deficiency has a negative influence on diverse pathological processes of angiogenesis, arteriogenesis and vascular leakage comprising ischemic retinopathy, tumor formation, pulmonary hypertension, vascular leakage (edema formation) and inflammatory disorders. The invention thus relates to molecules that can inhibit the binding of PIGF to its receptor (VEGFR-1), such as monoclonal antibodies and tetrameric peptides, and to the use of these molecules to treat the above-mentioned pathological processes.