This .STL design file is for a blood reservoir that can be easily integrated into the in vitro hemolysis testing of many medical devices. The three-piece reservoir consists of this 3D-printed base, along with a plastic clamp set and a hemocompatible blood bag. This simple, reusable, and cost-effective design has successfully been used in the hemolysis assessment of FDA benchmark nozzles and prototype rotary blood pumps, and it may be useful as an integral component to any in vitro blood circulation loop.