This invention relates to the treatment of neurological conditions with novel cyclic peptidic and peptidomimetic compounds which have the ability to modulate the activity of C5a receptors. The compounds preferably act as antagonists of the C5a receptor, and are active against C5a receptors on polymorphonuclear leukocytes, monocytes, lymphocytes and/or macrophages. In a preferred form of the invention the neurological conditions are neurodegenerative diseases, neuroimmunological disorders, diseases arising from dysfunction of the blood brain barrier, and stroke.