The City of Henderson, Nevada, is currently completing construction of one of the first ultraviolet (UV) disinfection facilities in the United States for water treatment. The City of Henderson (City) system was specifically designed to inactivate Cryptosporidium oocysts in a surface water supply. The City's schedule for implementation of advanced disinfection required that the system be designed and constructed prior to the development of specific guidance from the United States Environmental Projection Agency (USEPA). With these constraints, the City developed an approach to the implementation of UV disinfection that involved the Nevada State Health Division (NSHD) as a member of the project team. Based on the approach developed with the NSHD, the critical step in Henderson's implementation approach consists of UV system testing. With the equipment installed on- site, a three-step testing program will be completed that will culminate with on-site bioassays using one of the full-scale reactors to validate the performance capability of the UV equipment. In this paper, the issues associated with the full-scale, on-site testing planned at Henderson are described. Includes 10 references, figures.