To determine the most effective infection control procedure in preventing nosocomial infection with respiratory syncytial virus (RSV), we did a prospective controlled study of four infection-control strategies in four wards in a large paediatric hospital in the west of Scotland. All children under two years old admitted to four general wards during three winter RSV epidemics (1989-92) were screened for RSV infection (by nasopharyngeal aspirate and direct immunofluorescence) within 18 hours of admission. The main outcome measure was the occurrence of nosocomial infection, defined as the number of children initially RSV negative who became RSV positive 7 days or more after hospital admission (incubation period for RSV infection is 5-8 days). Without special precautions, there was a high rate of nosocomial RSV infection (26%). Nosocomial infection was significantly reduced by the combination of cohort nursing with the wearing of gowns and gloves for all contacts of RSV-infected children (p = 0.0022). Neither the use of gowns and gloves alone nor cohort nursing alone produced a significant reduction in cross-infection. In the final year, general clinical use of a policy of cohort nursing with gowns and gloves resulted in a reduction in the cross-infection rate by two-thirds of its original value (9.5% vs 26%). Combined with rapid laboratory diagnosis, cohort nursing and the wearing of gowns and gloves for all contacts with RSV-infected children can significantly reduce the risk of nosocomial RSV infection.