extent of reduction in microvessel density from 100 ug recombinant angiostatin is equivalent to 1 2 ug of angio 3 peptide based on this we estimated that angio 3 is at least as potent as angiostatin in inhibiting chick cam angiogenesis at high doses e g 1 mg cover slip the blood vessels under the cover slip containing all three peptides died and circulation was stopped the color of the blood changed into dark red instead of the bright red of the circulating blood the above data demonstrated that angio 2 angio 3 and angio 4 small peptides derived from the sequence of human plasminogen kringle domains 2 3 and 4 function as potent angiogenesis inhibitors importantly peptide angio 3 is more potent in inhibiting bae cell proliferation compared to angiostatin protein and at least as potent as recombinant angiostatin in inhibiting chick cam angiogenesis cao et al 12 show that integrity of complete kringle domains is required for anti angiogenic activity of angiostatin and that a tandem pair of properly folded domains is necessary cao et al 13 also show that at least with respect to the k5 domain appropriate disulfide bond formation is necessary for maintaining anti angiogenic activity thus it is surprising that the exemplified small peptides of the invention which 1 do not form complete kringle domains and 2 do.