The purpose of this article is to present the pioneering works in the field of environmental and energy economics by the Bulgarian economist Slavcho Zagorov (1898–1970) during the early 1950s, when Zagorov was in emigration. Zagorov is known to the Bulgarian reader as an economist and policy maker in the years between the two world wars. It is little known, however, that Zagorov was one of the first (his publications chronologically predate those of Nicolas Georgescu Roegen by about a decade) to present the concept of energy flow in the economy and human metabolism, explained through the prism of thermodynamics. Criticizing the traditional economic approach to national income from the point of view of "value", Zagorov developed a new energetic approach to national income and productivity. According to him, national income is a "movement of energy", which he calculates in terms of primary energy sources. The Bulgarian economist conducted a number of empirical studies on energy balances in the Danube Region, including in Bulgaria.