Species, known as mixture herbal products, are compositions of several types of crushed, sometimes whole, medicinal plant materials with additives; they are a widely used dosage form in the Russian Federation. A large range of species are produced at the pharmaceutical companies. In pharmacopoeial analysis, the most popular and widely used method for the determination of flavonoids, suitable for the standardization of species, is the method of differential spectrophotometry, based on the complexation of flavonoids with aluminum chloride. In accordance with modern requirements for the drugs production, the validation of analytical methods is a prerequisite for the creation of pharmacopoeial monographs projects regulating the quality of pharmaceutical substances of plant origin. Therefore, it is necessary to validate analytical methods for their intended use in evaluating the drug quality. This article discusses/presents the main stages of development and validation (by parameters: accuracy, precision, specificity, linearity) of the methodology for determining total flavonoid content using original species 'Fitourol' as a model. © 2019 Journal of Advanced Pharmaceutical Technology & Research Published by Wolters Kluwer - Medknow.