4,5-disubstituted-2-arylpyrimidines of Formula I and Formula II are provided: ##STR00001## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.8, R.sub.9, A and Ar are defined herein. Such compounds are ligands of C5a receptors. Preferred compounds of Formula I and II bind to C5a receptors with high affinity and exhibit neutral antagonist or inverse agonist activity at C5a receptors. The present invention also relates to pharmaceutical compositions comprising such compounds, and to the use of such compounds in treating a variety of inflammatory, cardiovascular, and immune system disorders. In addition, the present invention provides labeled 4,5-disubstituted-2-arylpyrimidines, which are useful as probes for the localization of C5a receptors.