Air filtration as a means of removing bacteria is reviewed to provide architects, engineers, hospital administrators, and research investigators with the benefit of information and experience gained. Various types of filters have been evaluated, using bacterial organisms aerosolized in particles with diameters of one to five microns as the test simulant. Based on results of these tests, filters have been placed into four categories: roughing (10 to 60% efficient), medium (60 to 90% efficient), high (90 to 99% efficient), and absolute (99.99+% efficient). Other methods of air purification, such as electrostatic precipitation, air washing, ultraviolet light, and incineration are mentioned briefly. Information is provided on filter evaluation methods, with most of the emphasis on biological techniques. Sections are included on factors to be considered in selecting filters for removal of bacterial particles and on installing and decontaminating filters.