This work presents a simple and fast method for the simultaneous determination of amiloride and furosemide by digital derivative spectrophotometry. HCl 1 x 10(-2) mol/l dissolved in ethanol was used as solvent and to extract drugs from formulations. Subsequently the samples were evaluated directly by first digital derivative spectrophotometry, using a smoothing factor of 8 and scale factor of 1 x 10(-4). The simultaneous determination of furosemide and amiloride can be carried out at 241.4 and 343.6 nm, respectively. In both cases, the zero crossing approach was used. When both compounds are present together in a sample, it is possible to quantify one in the presence of the other, without mutual interference. The determination range was found to be of 6.9 x 10(-8) to 16 x 10(-5) and 6.8 x 10(-8) to 8 x 10(-5) mol/l, for amiloride and furosemide, respectively. A good level of repeatability (RSD) of 0.9 and 0.6% was observed for amiloride and furosemide, respectively. The ingredients commonly found in commercial pharmaceutical formulations do not interfere. The proposed method was applied to the determination of these drugs in pharmaceutical formulations.