The effect of halides and different buffer anions on the quenching of the fluorescence of the new probe 10,10′-bis(3-sulfopropyl)-9,9′-biacridine (SPBA) has been studied using fluorescence and decay time measurements. The linearity of the Stern-Volmer plot indicates that fluorescence quenching by halides can be described reasonably well by a single-exponential decay with a K of 4.06 times 10⁶M⁻¹s⁻¹for chloride, 7.83 times 10⁶M⁻¹s⁻¹for bromide and 1.12 times 10⁷M⁻¹s⁻¹for iodide. We have found that SPBA is collisionally quenched also by the buffers 3-(N-mor-pholino)propanesulfonic acid (MOPS) and N-2-hydroxy-ethylpiperazine-N′-ethansulfonic acid (HEPES). The bi-molecular rate constants are 1.67 × 10⁶M⁻¹s⁻¹for HEPES and 1.44 times 10⁶M⁻¹s⁻¹for MOPS.