This article reviews Act 3,523 of the Brazilian Ministry of Health which regulates the indoor air quality of air-conditioned environments, focusing mainly on biological standards for contaminant particles. Additionally, a concise analysis on nosocomial air-borne infections is performed, as well as on nosocomial units where air-borne infectious diseases may be important and a special ventilation system is required. Detailed analysis of the most common biological contaminant particles, differences between countries of both Northern and Southern hemispheres, and the aspects of the methodology used to perform their analysis are considered. The authors conclude that there are no established standards for safe levels of air-borne organisms, and that there is no available data in Brazil to set up standards for biological contaminant particles

Keywords: Air pollutants. Air conditioning. Air quality standards. Indoor air pollution. Brazil.