To determine whether increased compliance with a policy of glove and gown isolation precautions could reduce the high rate of nosocomial respiratory syncytial virus (RSV) infection on an infant and toddler ward, we conducted a longitudinal intervention trial during three RSV seasons, from 1982 to 1985, with an intervention to increase compliance introduced midway through the second season. The risk of acquiring RSV infection in the hospital was adjusted for the intensity of nosocomial exposure to the virus by assigning each study week to one of five strata, defined by the proportion of hospital days on which virus was shed by children on the ward. Overall, 37 patients acquired nosocomial RSV infections during 7547 days at risk. The adjusted relative risk, comparing the infection rate in the period before the intervention (when compliance with isolation precautions was noted in only 38.5 percent of the observed patient contacts) with the infection rate in the postintervention period (when compliance more than doubled) was 2.9 (95 percent confidence interval, 1.5 to 5.7). Rates of nosocomial RSV infection increased linearly with increasing levels of exposure to patients shedding virus, but the rise in the infection rate with increasing exposure was less than one fourth as great (P less than 0.001) in the period after the intervention as it was before. We conclude that glove and gown precautions can substantially reduce the nosocomial transmission of RSV, particularly with increasing exposure to patients shedding the virus.