Hydrogen can be used for many different applications and can be integrated into many different system architectures. One of the methods for producing the hydrogen is to use an electrolyzer. This work explores the flexibility of electrolyzers to behave as responsive loads. Experimental tests were performed for a proton exchange membrane (PEM) and an alkaline electrolyzer to assess the operational flexibility of electrolyzers to behave as responsive loads. The results are compared to the operational requirements to participate in end-user facility energy management, transmission and distribution system support, and wholesale electricity market services. Electrolyzers begin changing their electricity demand within milliseconds of a set-point change. The settling time after a set-point change is on the order of seconds. It took 6.5 minutes for the PEM unit to execute a cold start and 1 minute to turn off. In addition, a frequency disturbance correction test was performed and electrolyzers were able to accelerate the speed that the grid frequency can be restored. Electrolyzers acting as demand response devices can respond sufficiently fast and for a long enough duration to participate in all of the applications explored. Furthermore, electrolyzers can be operated to support a variety of applications while also providing hydrogen for industrial processes, transportation fuel, or heating fuel. Additionally, favorable operating properties and a variety of potential system architectures showcase the flexibility of electrolyzer systems.