Presents a broad discussion of laboratories designed to provide high levels of biological containment (hot zone laboratories). Discusses the design issues encountered at Biosafety Levels 3 and 4 (BSL 3 and BSL 4) as defined in the CDC/NIH Guideline 'Biosafety in Microbiological and Biomedical Laboratories'. Stresses that a dialogue that takes a rational look at the engineering needs of these laboratories should be undertaken to allow them to be designed in a manner commensurate with the actual risk. In a separate section lists major HVAC requirements for BSL 3 and BSL 4.