Refractory High-Entropy Alloys (RHEAs) potentially offer enhanced properties and optimized performance in extreme conditions. Specifically, properties such as strength, radiation resistance, and corrosion resistance at high operating temperatures are of interest. To explore the compositional tailoring of RHEAs, high-throughput fabrication methods using metal additive manufacturing have been developed. Directed energy deposition, with four powder hoppers, was used for in situ alloying of elemental powders. The samples were based on Nb, Ta, Mo, and W. Over 50 alloy samples with different compositions can be fabricated in a few hours, permitting the development of high-throughput characterization methods for microstructural evolution and material properties. The methodology for elemental compositional control in the high-throughput alloying process, with an iterative technique, provides chemically uniform samples within 5% of the desired compositions. Moreover, because of the high cooling rates associated with the process, microsegregation distances have been reduced to approximately 2 microns.