[en] Central to the development of magnetic-mirror-confined fusion reactors is a clearer understanding of the influence of the neutral-beam injection process on such crucial aspects of the overall engineering design of such machines as the total system energy balance and the thermal/mechanical design of the first wall. While simple analytic and numeric models have proven useful in identifying the salient problem areas associated with the design of the integrated injector/plasma/wall system, a more thorough approach seems in order. To that end, a steady-state, 3-D Monte Carlo (MC) computer code has been developed and applied to the simulation of energetic neutral-beam injection into near-term mirror devices (e.g., the Mirror Experiment (MX) and the Fusion Engineering Research Facility (FERF)). Important plasma engineering information, heretofore unavailable, regarding the trapping of the neutral beam in the target plasma and the angular and energy distributions of the charge-transfer-produced neutral particle bombardment of the first wall has been obtained