The results of this preliminary investigation were unexpected but important in view of the increased use of probiotic preparations in medically fragile pediatric patients. In this randomized, placebo-controlled trial, L. rhamnosus strain GG was not shown to be effective in reducing the incidence of nosocomial infections. In fact, a statistically nonsignificant trend toward an increase in infection was seen (four vs. 11). Further studies with a larger patient population are needed to establish both safety and efficacy of probiotics in pediatric critical care.