The invention relates to the use of an agent that promotes class III SLRP activity in the manufacture of a medicament for the inhibition of blood vessel formation. In addition the invention relates to the use of an agent that promotes class III SLRP activity in the manufacture of a medicament for the prevention and/or treatment of conditions characterised by excessive activity and/or migration of monocytes and/or macrophages. Suitable agents may include class III SLRPs such as opticin. Methods of treatment using agents able to promote class III SLRP activity are also provided.