UNLABELLED:Respiratory syncytial virus (RSV) chest infection is a common cause of hospitalization in the very young child. The aim of this study was to determine the direct cost of resource utilization in the treatment of children hospitalized with RSV chest infection and the potential cost-savings with passive immunization for high-risk infants. An audit of the hospital resource consumption and its costs was performed for 216 children aged < 24 mo admitted with RSV chest infection between 1995 and 1997. The cost-saving potential of passive immunization using monoclonal RSV antibodies during the RSV season was determined by assuming an 0.55 efficacy in hospitalization reduction when administered to "high-risk" infants according to the guidelines outlined by the American Academy of Pediatrics (AAP). The hospital treatment cost of 1064 bed-days amounted to USD 64 277.70. Each child occupied a median of 4.0 bed-days at a median cost of USD 169.99 (IQ1 128.08, IQ3 248.47). Children, who were ex-premature or with an underlying illness were more likely to have a longer hospital stay, higher treatment costs and need for intensive care. Ten (42%) of 24 ex-premature infants fulfilled the recommended criteria for passive immunization. Its use resulted in an incremental cost of USD 31.39 to a potential cost saving of USD 0.91 per infant for each hospital day saved. CONCLUSION:Ex-prematurity and the presence of an underlying illness results in escalation of the direct treatment cost of RSV chest infection. Current guidelines for use of passive RSV immunization do not appear to be cost-effective if adopted for Malaysian infants.