The article focuses on assessing the differences between Russian regions in terms of shadow economy level, these are important to take into account when studying such phenomena as behavior of taxpayers, tax compliance and tax evasion. The purpose of this article is to find differences in the level of the shadow economy between the regions of the Russian Federation and to specify their impact on the methodology for carrying out experimental studies into the behavior of taxpayers. Experimental study methods of behavior of taxpayers have been widely used since the second quarter of the 20th century, but most of the described tax experiments relate to European countries and the USA, which have a relatively high level of tax compliance and tax discipline. The study of the behavior of taxpayers in countries with a different level of tax discipline, in particular in Russia, may be of interest. To take into account the differences in the scale of tax evasion and the level of the shadow economy in different regions of Russia, a methodology was developed to measure the size of the shadow economy in the regions on the basis of a comparison of statistical and tax reporting data. The data presented show the heterogeneity of the Russian regions in terms of shadow sector share, as well as the heterogeneity of entrepreneurs and the population of different regions in their tendency to evade taxes. These circumstances should be taken into account when conducting tax experiments in various regions of the country.