As part of a preliminary design for a 2,000 mgd ultraviolet light (UV) disinfection facility for the City of New York, computer models have been used to predict the effectiveness of UV reactors at inactivating pathogens with the goal of using the models to validate full-scale UV reactors. The New York City Department of Environmental Protection (DEP) has developed a protocol for validation of UV reactors through computer modeling (Valade 2003). The protocol includes two phases of work. The initial phase is complete, and demonstrated that modeling could be used to predict the performance of the Wedeco K3000 low pressure, high intensity (LPHI) reactor, validated at the DVGW Testing Facility (Rokjer 2002). The second phase of the protocol is to model one larger LPHI reactor, and extend the models to include several medium pressure (MP) reactors of differing capacities and configurations, all of which have been validated through biodosimetry. This paper presents the results of the modeling of two Trojan medium pressure reactors as part of a larger modeling program. Includes 16 references, tables, figures.