Respiratory syncytial virus (RSV) is responsible for serious respiratory disease in young infants. More than 75% of the 678 children hospitalized for RSV at Baylor-affiliated hospitals in Houston, TX, between October 1992, and March, 1993, were 5 months of age or younger. The importance of maternal antibody in the immunity against RSV disease has been debated. More recent epidemiologic studies have demonstrated protection against RSV in babies born to mothers with high levels of neutralizing RSV antibody. The contribution of IgC fusion or F protein antibody as a correlate with immunity from disease also has been described. With the availability of purified F protein vaccines such as the purified F protein vaccines manufactured by Lederle-Praxis-Biologeals (Pearl River, NY), immunization of pregnant women with RSV surface glycoproteins to arm the newborn with high neutralizing antibody can be considered. Advantages of maternal immunization to augment naturally occurring maternal RSV antibody are that babies most at risk for infection are least responsive to vaccines, that pregnant women respond well immunologically to vacciaes in general and that placental transfer of maternal IgG antibody occurs naturally during the third trimester. The safety of maternally derived antibody would likely surpass that of exogenously administered immunoglobulin as well as would have a decreased cost. Disadvantages of maternal immunization to protect infants against RSV could include the potential inhibition of the infant's response to active immunization or subsequent disease, the lack of antibody transfer in premature infants, and liability issues. Evaluation of purified F protein vaccine in postpartum women is under way.