A series of aniline-substituted tetrahydroquinoline C5a receptor antagonists were discovered. A functionality requirement of ortho substitution on the aniline was revealed. Secondary anilines, in general, outperformed tertiary analogs in inhibition of C5a-induced calcium mobilization. Further enhancement of activity was realized in the presence of an ortho hydroxyalkyl side chain. The functional IC(50) of selected analogs was optimized to the single-digit nanomolar level.