The concept of indirect fluorometry for detection in ion chromatography is presented. A fluorescing eluting ion is used to maintain a constant background signal. When the analyte ions elute, electroneutrality forces the displacement of an equivalent amount of the eluting ions at the detector. A decrease in signal is then observed. A mass detectability of 6.7 ng of chloride ion is obtained (S/N = 3), which corresponds to a concentration detectability of 7.5 x 10/sup -8/ N. This is possible due to a novel double-beam arrangement for laser-excited fluorescence, substantially reducing the flicker noise. 18 references, 3 figures.