Twenty-four acridine derivatives were screened for trypanocidal activity in Trypanosoma brucei in order to determine which structural features of the acridine molecule confer maximal antiparasitic activity. The syntheses of several new azidoacridine derivatives are also reported as well as an assessment of their value as possible photoaffinity probes for the study of acridine trypanocidal action. The most effective and selective acridine trypanocides, with and without irradiation, were the 3-amino-10-methylacridinium salt derivatives. With brief irradiation, one azidoacridine, 3-amino-6-azido-10-methylacridinium chloride, showed considerable trypanocidal activity at very limiting drug concentrations (10-7 M) and warrants consideration as a possible photoaffinity probe. © 1984, American Chemical Society. All rights reserved.