An electrochemiluminescence (ECL) inhibition method was developed as an indirect detection method for the determination of dopamine and epinephrine separated by capillary electrophoresis (CE). When the concentration of Ru(bpy)(3)(2+) was 50 μ m diluted by 50 mm phosphate (pH 8.5) in the cell and 0.5 m tripropylamine (TPA) was added to the running buffer (10 mm phosphate, pH 9.0), an inhibition of ECL of the Ru(bpy)(3)(2+)/ TPA system by the analytes was observed. Under the optimized conditions, the relative standard deviations of migration time and negative peak area were less than 1% and 3%, respectively, for 1 μ m dopamine or 1 μ m epinephrine (n = 10). Linear ranges of 0.1-10 μ m for both analytes and the detection limits (signal-to-noise ratio S/N = 3) of 10 nm for dopamine and 30 nm for epinephrine were obtained.