A method based on the peak obtained by adsorptive stripping voltammetry for the complex formed by organic matter in the presence of trace amounts of molybdenum(VI) has been tested for the determination of refractory organic matter, the so-called humic substances, in freshwaters. The method is rapid and particularly well-adapted to the determination of low amounts of refractory organic matter. It has a detection limit of 2.4gCL−1 for 3 min deposition time. The effect of the presence of other types of natural organic matter has been tested. The method has been applied to a wide variety of freshwaters at different trophic states.