Barrier precautions are a fundamental component of any infection control strategy and a critical aspect of all isolation systems. Because many infections are transmitted from patient-to-patient via the hands of personnel, gloves and gowns are widely recommended to provide an extra measure of protection against cross-infection. It is not clear whether gloves are superior to handwashing (if performed obsessionally) in this respect, and there is little evidence that gowns confer additional benefit. These concerns notwithstanding, barrier precautions can substantially reduce the risk of some infections, such as respiratory syncytial virus disease. On the other hand, the modes of transmission of many infections are complex (e.g. with rotavirus) or controversial (e.g. with rhinovirus), and, even though hands are involved in transmission, barrier precautions alone may not suffice to prevent spread. Moreover, neither gloves nor gowns can prevent nosocomial infections caused by endogenous microbial flora; perhaps this explains the limited efficacy of barrier precautions in reducing the endemic rate of infection due to bacteria such as Pseudomonas aeruginosa in intensive care units. Barrier precautions may also fail if colonized patients are not identified promptly. One potential solution to this problem is \'body substance isolation\' (BSI), in which all patients are considered to be potential carriers of nosocomial pathogens whether or not they have been cultured or have developed a clinical infection. In BSI barrier techniques are used when any potentially contaminated patient material is handled. BSI also provides barrier protection from bloodborne pathogens for personnel.(ABSTRACT TRUNCATED AT 250 WORDS)