The Chemical Reaction Network Toolbox provides computer-supported assistance for the analysis of the behavior of complex chemical reaction networks. Its use and theoretical underpinnings are described, for example, in the monograph "Foundations of Chemical Reaction Network Theory" by Martin Feinberg, published in 2019 by Springer-Nature. The download is a zip file containing the Toolbox, a user's guide, and some sample network files. There is also a text file containing installation instructions. This is the legacy DOS version of the Toolbox. The more modern and far more theoretically capable Windows version is available at https://doi.org/10.5281/zenodo.5149266. However, the DOS version has capabilities of its own, in particular a powerful simulation environment. The DOS version will run on Windows, Macintosh, or Linux computers by means of the freely available DOSBox emulation software: https://www.dosbox.com.