One of the main concerns for healthcare building design is how to prevent the dispersion of airborne infectious diseases such as tuberculosis. Moreover, it is suspected that fungi and bacteria growing in air handling units (AHUs) can also cause respiratory diseases in building occupants. Ultraviolet germicidal irradiation (UVGI) systems have been known to have an apparent germicidal effect on infectious microbes and have been considered as a possible countermeasure. In this presentation, some results achieved from a series of laboratory and field experiments and numerical evaluations using the concept of ventilation efficiency will be introduced. In this process, the performance and the limitation of UVGI systems in building applications will be discussed.