The invention provides an ±5²1 antagonist agent which comprises a non-peptide organic molecule or a peptide for use in reducing or inhibiting angiogenesis in a tissue by a method comprising contacting ±5²1 integrin in the tissue with said agent, thereby reducing or inhibiting angiogenesis in the tissue. The invention also provides an ±5²1 antagonist agent which comprises a non-peptide organic molecule or a peptide for use in diagnosing a pathological condition characterized by angiogenesis in a tissue in an individual, by a method comprising the steps of: (a) administering said ±5²1 antagonist agent to an individual suspected of having the pathological condition； and (b) detecting specific binding of the agent to ±5²1 integrin associated with a blood vessel in the tissue, thereby diagnosing a pathological condition characterized by angiogenesis in the individual.
