Reactive dyes, such as Procion Yellow, Procion Red, and Procion Blue, were simultaneously determined in aqueous ternary solutions using derivative cathodic stripping voltammetry following adsorption on a hanging mercury drop electrode. An electrochemical cell containing Britton–Robinson buffer solution at pH 8 was used as the supporting electrolyte. The following experimental conditions were established: −0.100 V deposition potential, 80 s deposition time, 50 mV pulse amplitude, 50 mV s−1 scan rate, and 0.40 mm2 maximum mercury drop size. A linear response was observed over the 0.630 × 10−3 to 1.050, 1.441 × 10−3 to 1.572, and 0.198 to 1.570 mg l−1 ranges for Procion Yellow, Procion Red, and Procion Blue respectively. The detection limits were 0.210 × 10−3, 0.480 × 10−3, and 0.066 mg l−1 respectively, with a relative standard deviation (n = 3) of 1.22%. The accuracy of the method was evaluated by derivative spectrophotometry, certifying the results as a function of proximity. All results were similar, indicating that derivative cathodic stripping voltammetry may be efficiently applied for the simultaneous determination of textile dyes in aqueous ternary solutions.