The most common method in the routine determination of uronic acids, the m-hydroxydiphenyl reaction, recently adapted to rapid microplate analysis, has as a main inconvenience, in any one of their modalities, interferences due to the frequent presence of proteins and neutral carbohydrates in the samples. Corresponding corrections in the literature are unsatisfactory when applied to complex matrices, and further adaptation to the microplate analysis is not free from additional problems. With particular reference to hyaluronic acid, the interactions between the principal reactants and the interfering materials are studied kinetically under realistic conditions, and simple mathematical models are proposed which satisfactorily describe the experimental results and allow adequate corrections to be made.