This invention relates to low molecular weight, non-peptidic, non-peptidomimetic, organic molecules that act as modulators of mammalian complement C5a receptors, preferably ones that act as high affinity C5a receptor ligands and also to such ligands that act as antagonists or inverse agonists of complement C5a receptors. Preferred compounds of the invention possess some or all of the following properties in that they are: 1) multi-aryl in structure, 2) heteroaryl in structure, 3) a pharmaceutically acceptable oral dose can provide a detectable in vitro effect, 4) comprise fewer than four or preferably no amide bonds, and 5) capable of inhibiting leukocyte chemotaxis at nanomolar or sub-nanomolar concentrations.This invention also relates to pharmaceutical compositions comprising such compounds and the use of such compounds in treating a variety of inflammatory and immune system disorders. Additionally, this invention relates to the use such compounds as probes for the localization of C5a receptors.